The outstanding comprehensive mechanical properties of newly developed hybrid lattice structures make them useful in engineering applications for bearing multiple mechanical loads.Additive-manufacturing technologies m...The outstanding comprehensive mechanical properties of newly developed hybrid lattice structures make them useful in engineering applications for bearing multiple mechanical loads.Additive-manufacturing technologies make it possible to fabricate these highly spatially programmable structures and greatly enhance the freedom in their design.However,traditional analytical methods do not sufficiently reflect the actual vibration-damping mechanism of lattice structures and are limited by their high computational cost.In this study,a hybrid lattice structure consisting of various cells was designed based on quasi-static and vibration experiments.Subsequently,a novel parametric design method based on a data-driven approach was developed for hybrid lattices with engineered properties.The response surface method was adopted to define the sensitive optimization target.A prediction model for the lattice geometric parameters and vibration properties was established using a backpropagation neural network.Then,it was integrated into the genetic algorithm to create the optimal hybrid lattice with varying geometric features and the required wide-band vibration-damping characteristics.Validation experiments were conducted,demonstrating that the optimized hybrid lattice can achieve the target properties.In addition,the data-driven parametric design method can reduce computation time and be widely applied to complex structural designs when analytical and empirical solutions are unavailable.展开更多
In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,ef...In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.展开更多
Based on superelastic damping application in structural engineering, the damping characteristics of commercial Ti-50.8Ni(mole fraction, %) alloy have been systematically studied by adjusting frequency of mechanical sh...Based on superelastic damping application in structural engineering, the damping characteristics of commercial Ti-50.8Ni(mole fraction, %) alloy have been systematically studied by adjusting frequency of mechanical shock, temperature, stress, strain and number of cycling. The results show that at extremely low frequency mechanical shock at room temperature, the superelastic damping capacity increases with controlled strain, and such capacity of each cycle is greater than 50%. When the frequency of mechanical shock is 0.10.3 Hz, the superelastic damping capacity above room temperature is relatively large at high strain; when the temperature approaches to M_d, the damping begins at low stress. For specimen cycled under 0.5 Hz, above 6% strain mechanical shock at relatively high temperature, further large-strain cycling exhibits more than 35% damping capacity. The superelastic damping of trained specimen is relatively stable at 2050 ℃ and 0.10.5 Hz frequency mechanical shock.展开更多
Co2MnSi thin films are made by magnetron sputtering onto MgO （001） substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550℃ and...Co2MnSi thin films are made by magnetron sputtering onto MgO （001） substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550℃ and subsequently annealed at 550℃ （sample I） exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on.展开更多
<span style="font-family:Verdana;">In this paper, for the initial and boundary value problem of beams with</span> <span style="font-family:Verdana;">structural damping, by introdu...<span style="font-family:Verdana;">In this paper, for the initial and boundary value problem of beams with</span> <span style="font-family:Verdana;">structural damping, by introducing intermediate variables, the original </span><span style="font-family:Verdana;">fourth-order problem is transformed into second-order partial differential equations, and the mixed finite volume element scheme is constructed, and the existence, uniqueness and convergence of the scheme are analyzed</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span><span><span><span style="font-family:Verdana;"> Numerical examples are provided to confirm the theoretical results. In the end, we test the value of <em>δ</em></span><span style="font-family:Verdana;"> to observe its influence on the model.</span></span></span>展开更多
Based on energy dissipation and structural control principle, a new structural configuration, called the megasub controlled structure （MSCS） with friction damped braces （FDBs）, is first presented. Meanwhile, to ca...Based on energy dissipation and structural control principle, a new structural configuration, called the megasub controlled structure （MSCS） with friction damped braces （FDBs）, is first presented. Meanwhile, to calculate the damping coefficient in the slipping state a new analytical method is proposed. The damping characteristics of one-storey friction damped braced frame （FDBF） are investigated, and the influence of the structural parameters on the energy dissipation and the practical engineering design are discussed. The nonlinear dynamic equations and the analytical model of the MSCS with FDBs are established. Three building structures with different structural configurations, which were designed with reference to the conventional mega-sub structures such as used in Tokyo City Hall, are comparatively investigated. The results illustrate that the structure presented in the paper has excellent dynamic properties and satisfactory control effectiveness.展开更多
An optimization method for the consistent evaluation of two Rayleigh damping coefficients is proposed. By minimizing an objective function such as an error term of the peak displacement of a structure, the two coeffic...An optimization method for the consistent evaluation of two Rayleigh damping coefficients is proposed. By minimizing an objective function such as an error term of the peak displacement of a structure, the two coefficients can be determined with response spectral analysis. The optimization method degenerates into the conventional method used in current practices when only two modes of vibration are included in the objective function. Therefore, the proposed method with all significant modes included for simplicity in practical applications results in suboptimal damping coefficients. The effects of both spatial distribution and frequency content of excitations as well as structural dynamic characteristics on the evaluation of Rayleigh damping coefficients were investigated with a five-story building structure. Two application examples with a 62-story high-rise building and a 840 m long cable-stayed bridge under ten earthquake excitations demonstrated the accuracy and effectiveness of the proposed method to account for all of the above effects.展开更多
Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structu...Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structural characteristics under normal environmental loadings and their behavior under dynamic loadings. In this research, a typical Tibetan wooden wall-frame building is selected to study its dynamic characteristics. Field measurements of the structure were conducted under environmental excitation to collect acceleration responses. The stochastic subspace identification （SSI） method was adopted to calculate the structural modal parameters and obtain the out-of-plane vibration characteristics of the slab and frames. The results indicated that the wall-frame structure had a lower out-of-plane stiffness and greater in-plane stiffness due to the presence of stone walls. Due to poor identified damping ratio estimates from the SSI method, a method based on the variance upper bound was proposed to complement the existing variance lower bound method for estimating the modal damping ratio to address the significant damping variability obtained from different points and measurements. The feasibility of the proposed method was illustrated with the measured data from the floor slab of the structure. The variance lower and upper bound methods both provided consistent results compared to those from the traditional SSI method.展开更多
Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using ...Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using a rubber-sand-concrete(RSC)as the aseismic material,is proposed.The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests.The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis,composite loss factor and damping ratio of the transfer function analysis,and total vibration level of octave spectrum analysis were discussed.The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear,and that the hollow damping layer had a better aseismic performance than the flat damping layer one.The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated.The effects of the peak ground acceleration(PGA)and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain(PEEQ)were discussed.The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance,with PGA in the range(0.2-1.2)g and tunnel overburden depth in the range of 0-300 m.展开更多
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
Hunting stability is an important performance criterion in railway vehicles.This study proposes an incorporation of a bio-inspired limb-like structure(LLS)-based nonlinear damping into the motor suspension system for ...Hunting stability is an important performance criterion in railway vehicles.This study proposes an incorporation of a bio-inspired limb-like structure(LLS)-based nonlinear damping into the motor suspension system for traction units to improve the nonlinear critical speed and hunting stability of high-speed trains(HSTs).Initially,a vibration transmission analysis is conducted on a HST vehicle and a metro vehicle that suffered from hunting motion to explore the effect of different motor suspension systems from on-track tests.Subsequently,a simplified lateral dynamics model of an HST bogie is established to investigate the influence of the motor suspension on the bogie hunting behavior.The bifurcation analysis is applied to optimize the motor suspension parameters for high critical speed.Then,the nonlinear damping of the bio-inspired LLS,which has a positive correlation with the relative displacement,can further improve the modal damping of hunting motion and nonlinear critical speed compared with the linear motor suspension system.Furthermore,a comprehensive numerical model of a high-speed train,considering all nonlinearities,is established to investigate the influence of different types of motor suspension.The simulation results are well consistent with the theoretical analysis.The benefits of employing nonlinear damping of the bio-inspired LLS into the motor suspension of HSTs to enhance bogie hunting stability are thoroughly validated.展开更多
A realistic and economical dynamic assessment of railway bridges requires input parameters that correspond to reality.In this context,the applied damping properties of the structure have a decisive influence on the re...A realistic and economical dynamic assessment of railway bridges requires input parameters that correspond to reality.In this context,the applied damping properties of the structure have a decisive influence on the results in the prediction of resonance effects and further in the assessment of the compatibility between rolling stock and railway bridges.The standard prescribes damping factors depending on the type of structure and the span to be used in dynamic calculations.However,these factors can be regarded as very conservative values which do not represent reality.Thus,in situ measurements on the structure are often necessary to classify a bridge categorised as critical in prior dynamic calculations as non-critical.Regarding in situ tests,a measurement-based determination of the damping factor is inevitably accompanied by a scattering of the generated results due to the measurement method used and as a result of the individual scope of action of the test-evaluating person and this person’s interpretation of the measurement data.This paper presents novel evaluation methods and analysis tools for determining the damping factor based on measurements in the frequency and time domains,intending to reduce the scatter of the results and limit the scope of action of the person evaluating the test.The main aim is to provide simple and easy-to-use evaluation algorithms for practical applications without additional data transformations and to define clear principles of action for the data-based evaluation of realistic and high damping factors.Based on in situ tests on 15 existing railway bridges,the data-based procedure for determining the damping factor is explained,and the methods are compared in the time and frequency domains.It is shown that a clearly defined evaluation algorithm can significantly reduce the scattering of results.Furthermore,it is demonstrated that forced vibration excitation and evaluation in the frequency domain provide the best results in reliable,reproducible,and high damping factors.展开更多
The methods of modifying dimension and shape of structure, or covering damping material are effective to reduce structure-borne noise, while these methods are based on the knowledge of qualitative and quantitative rel...The methods of modifying dimension and shape of structure, or covering damping material are effective to reduce structure-borne noise, while these methods are based on the knowledge of qualitative and quantitative relationship between sound radiation and design parameters. In order to decrease the complexity of the problem, response surface method(RSM) was utilized to analyze and optimize the vibro-acoustic properties of the damping structure. A simple case was illustrated to demonstrate the capabilities of the developed procedure. A structure-born noise problem was approximated by a series of polynomials using RSM. Three main performances were considered, i.e. sound radiation power, first order modal frequency and total mass. Consequently, the response surface model not only gives the direction of design modification, it also leads to an optimal design of complex systems.展开更多
The stress strain curves of two CuZnAl shape memory alloys which have the martensitic transformation temperatures of 50 ℃ and -10 ℃ respectively, were measured by using electronic material tester after treated by di...The stress strain curves of two CuZnAl shape memory alloys which have the martensitic transformation temperatures of 50 ℃ and -10 ℃ respectively, were measured by using electronic material tester after treated by different heat-treatment conditions. The results show that the area enclosed by hysteresis loop of the CuZnAl shape memory alloy in martensitic state is much larger than that of the alloy in austenitic state with super-elasticity at room temperature. Therefore, the former has better vibration attenuation effect. After being oil-quenched, water-quenched, and step-quenched, the CuZnAl alloy takes on more stable shape memory effect,better super-plasticity and superelasticity (pseudoelasticity). A CuZnAl shape memory alloy damper was designed, produced and installed to a 2-layer frame structure. In addition, the vibration experiments were made by dynamic data collecting analysis meter. The velocity of vibration attenuation of frame structure with CuZnAl shape memory alloy damper is much faster than that without it. And with the help of CuZnAl shape memory alloy damper, the attenuation period reduces to 1/10 of the original.展开更多
This study examines the roles of soil-structure interaction （SSI）, higher modes, and damping in a base-isolated structure built on multiple layers of soil overlying a half space. Closed-form solutions for the entire...This study examines the roles of soil-structure interaction （SSI）, higher modes, and damping in a base-isolated structure built on multiple layers of soil overlying a half space. Closed-form solutions for the entire system, including a superstructure, seismic isolator, and numerous soil layers overlying a half-space, were obtained. The formulations obtained in this study simply in terms of well-known frequencies and mechanical impedance ratios can explicitly interpret the dynamic behavior of a base-isolated structure interacting with multiple soil layers overlying a half-space. The key factors influencing the performance of the isolation system are the damping ratio of the isolator and the ratio of the natural frequency of the fixed-base structure to that of the isolated structure by assuming that the superstructure moves as a rigid body. This study reveals that higher damping in the base isolator is unfavorable to higher mode responses that usually dominate the responses of the superstructure and that the damping mechanism plays an important role in transmitting energy in addition to absorbing energy. It is also concluded that it is possible to design a soft soil layer as an isolation system for isolating vibration energy.展开更多
The damping material optimal placement for the structure with damping layer is studied based on evolutionary structural optimization (ESO) to maximize modal loss factors. A mathematical model is constructed with the o...The damping material optimal placement for the structure with damping layer is studied based on evolutionary structural optimization (ESO) to maximize modal loss factors. A mathematical model is constructed with the objective function defined as the maximum of modal loss factors of the structure and design constraints function defined as volume fraction of damping material. The optimal placement is found. Several examples are presented for verification. The results demonstrate that the method based on ESO is effective in solving the topology optimization of the structure with unconstrained damping layer and constrained damping layer. This optimization method suits for free and constrained damping structures.展开更多
Three kinds of different phases of Mg-xLi-1Al alloys with x=5 （full α LA51）, 9 （dual-phase LA91）, and 14 （rich-βLA141） were prepared by vacuum melting method. Their microstructure and damping capacities were i...Three kinds of different phases of Mg-xLi-1Al alloys with x=5 （full α LA51）, 9 （dual-phase LA91）, and 14 （rich-βLA141） were prepared by vacuum melting method. Their microstructure and damping capacities were investigated by optical microscopy, X-ray diffractometry, and dynamic mechanical analysis. The results show that the addition of Li changes the crystal structure of the alloys and causes new damping mechanisms to emerge. And the appearance of BCC structure makes the damping performance improved remarkably. The lower the elastic modulus is, the smaller the strain is and even the slower the acceleration is. The dual-phase alloy shows a better damping capacity while the temperature changes. Furthermore, all three alloys have two significant peaks：P1 caused by the movement of dislocations on the basal planes and P2 caused by the sliding of grain boundaries.展开更多
A method to calculate the stationary random response of a non-classically damped structure is proposed that features clearly-defined physical meaning and simple expression. The method is developed in the frequency dom...A method to calculate the stationary random response of a non-classically damped structure is proposed that features clearly-defined physical meaning and simple expression. The method is developed in the frequency domain. The expression of the proposed method consists of three terms, i.e., modal velocity response, modal displacement response, and coupled (between modal velocity and modal displacement response). Numerical results from the parametric study and three example structures reveal that the modal velocity response term and the coupled term are important to structural response estimates only for a dynamic system with a tuned mass damper. In typical cases, the modal displacement term can provide response estimates with satisfactory accuracy by itself, so that the modal velocity term and coupled term may be ignored without loss of accuracy. This is used to simplify the response computation of non-classically damped structures. For the white noise excitation, three modal correlation coefficients in closed form are derived. To consider the modal velocity response term and the coupled term, a simplified approximation based on white noise excitation is developed for the case when the modal velocity response is important to the structural responses. Numerical results show that the approximate expression based on white noise excitation can provide structural responses with satisfactory accuracy.展开更多
By analyzing the correlation between modal calculations and modal experiments of a typical supporter, an effective finite element analysis( FEA)model of the actual aerospace supporter is created. According to the anal...By analyzing the correlation between modal calculations and modal experiments of a typical supporter, an effective finite element analysis( FEA)model of the actual aerospace supporter is created. According to the analysis of constrained viscoelastic damping, the strategies of PVC have been worked out, and the correlation between modal calculations and modal experiments of the supporter has also been computed, and then, an experiment has been designed based on the calculation results. The results of experiments verify that the PVC strategy can effectively suppress vibration.展开更多
基金supported by National Natural Science Foundation of China(Grant No.52375380)National Key R&D Program of China(Grant No.2022YFB3402200)the Key Project of National Natural Science Foundation of China(Grant No.12032018).
文摘The outstanding comprehensive mechanical properties of newly developed hybrid lattice structures make them useful in engineering applications for bearing multiple mechanical loads.Additive-manufacturing technologies make it possible to fabricate these highly spatially programmable structures and greatly enhance the freedom in their design.However,traditional analytical methods do not sufficiently reflect the actual vibration-damping mechanism of lattice structures and are limited by their high computational cost.In this study,a hybrid lattice structure consisting of various cells was designed based on quasi-static and vibration experiments.Subsequently,a novel parametric design method based on a data-driven approach was developed for hybrid lattices with engineered properties.The response surface method was adopted to define the sensitive optimization target.A prediction model for the lattice geometric parameters and vibration properties was established using a backpropagation neural network.Then,it was integrated into the genetic algorithm to create the optimal hybrid lattice with varying geometric features and the required wide-band vibration-damping characteristics.Validation experiments were conducted,demonstrating that the optimized hybrid lattice can achieve the target properties.In addition,the data-driven parametric design method can reduce computation time and be widely applied to complex structural designs when analytical and empirical solutions are unavailable.
文摘In this paper,a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested.This new system amplifies the structural displacement to dissipate more energy,and in turn,effectively reduces the structural response in the case of relatively small story drifts,which occur during earthquakes.A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted.From the experimental and analytical results,it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response,requires less energy input,operates with higher reliability,and can be manufactured at a lower cost and used in a wider range of engineering applications.
文摘Based on superelastic damping application in structural engineering, the damping characteristics of commercial Ti-50.8Ni(mole fraction, %) alloy have been systematically studied by adjusting frequency of mechanical shock, temperature, stress, strain and number of cycling. The results show that at extremely low frequency mechanical shock at room temperature, the superelastic damping capacity increases with controlled strain, and such capacity of each cycle is greater than 50%. When the frequency of mechanical shock is 0.10.3 Hz, the superelastic damping capacity above room temperature is relatively large at high strain; when the temperature approaches to M_d, the damping begins at low stress. For specimen cycled under 0.5 Hz, above 6% strain mechanical shock at relatively high temperature, further large-strain cycling exhibits more than 35% damping capacity. The superelastic damping of trained specimen is relatively stable at 2050 ℃ and 0.10.5 Hz frequency mechanical shock.
基金Supported by the National Basic Research Program of China under Grant No 2015CB921502the National Natural Science Foundation of China under Grant Nos 11474184 and 11174183+3 种基金the 111 Project under Grant No B13029the Natural Science Foundation of Shandong Province under Grant No JQ201201the Doctorate Foundation of Shandong Province under Grant No BS2013CL042the Young Scientists Fund of the National Natural Science Foundation of China under Grant No 11204164
文摘Co2MnSi thin films are made by magnetron sputtering onto MgO （001） substrates. The crystalline quality is improved by increasing depositing temperature and/or annealing temperature. The sample deposited at 550℃ and subsequently annealed at 550℃ （sample I） exhibits a pseudo-epitaxial growth with partially ordered L21 phase. Sample I shows a four-fold magnetic anisotropy, in addition to a relatively weak uniaxial anisotropy. The Gilbert damping factor of sample I is smaller than 0.001, much smaller than reported ones. The possible reasons responsible for the small Gilbert damping factor are discussed, including weak spin-orbit coupling, small density of states at Fermi level, and so on.
文摘<span style="font-family:Verdana;">In this paper, for the initial and boundary value problem of beams with</span> <span style="font-family:Verdana;">structural damping, by introducing intermediate variables, the original </span><span style="font-family:Verdana;">fourth-order problem is transformed into second-order partial differential equations, and the mixed finite volume element scheme is constructed, and the existence, uniqueness and convergence of the scheme are analyzed</span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.</span></span></span><span><span><span style="font-family:Verdana;"> Numerical examples are provided to confirm the theoretical results. In the end, we test the value of <em>δ</em></span><span style="font-family:Verdana;"> to observe its influence on the model.</span></span></span>
基金Science and Technology Fund of NWPU Under Grant No. M450211 Seed Fund of NWPU Under Grant No. Z200729
文摘Based on energy dissipation and structural control principle, a new structural configuration, called the megasub controlled structure （MSCS） with friction damped braces （FDBs）, is first presented. Meanwhile, to calculate the damping coefficient in the slipping state a new analytical method is proposed. The damping characteristics of one-storey friction damped braced frame （FDBF） are investigated, and the influence of the structural parameters on the energy dissipation and the practical engineering design are discussed. The nonlinear dynamic equations and the analytical model of the MSCS with FDBs are established. Three building structures with different structural configurations, which were designed with reference to the conventional mega-sub structures such as used in Tokyo City Hall, are comparatively investigated. The results illustrate that the structure presented in the paper has excellent dynamic properties and satisfactory control effectiveness.
基金National Natural Science Foundation of China under Grant No.51078032the Visiting Scholar Foundation of China Scholarship Councilthe Center for Infrastructure Engineering Studies at Missouri University of Science and Technology
文摘An optimization method for the consistent evaluation of two Rayleigh damping coefficients is proposed. By minimizing an objective function such as an error term of the peak displacement of a structure, the two coefficients can be determined with response spectral analysis. The optimization method degenerates into the conventional method used in current practices when only two modes of vibration are included in the objective function. Therefore, the proposed method with all significant modes included for simplicity in practical applications results in suboptimal damping coefficients. The effects of both spatial distribution and frequency content of excitations as well as structural dynamic characteristics on the evaluation of Rayleigh damping coefficients were investigated with a five-story building structure. Two application examples with a 62-story high-rise building and a 840 m long cable-stayed bridge under ten earthquake excitations demonstrated the accuracy and effectiveness of the proposed method to account for all of the above effects.
基金National Natural Science Foundation of China under Grant No.51338001Natural Science Foundation of China under Grant Nos.51178028 and 51422801+2 种基金the Fundamental Research Funds for the Central Universities under Grant No.2014YJS087Program for New Century Excellent Talents in University under Grant No.NCET-11-0571111 Project of China under Grant No.B13002
文摘Tibetan heritage buildings have a high historical and cultural value. They have endured adverse environmental loadings over hundreds of years without significant damage. However, there are few reports on their structural characteristics under normal environmental loadings and their behavior under dynamic loadings. In this research, a typical Tibetan wooden wall-frame building is selected to study its dynamic characteristics. Field measurements of the structure were conducted under environmental excitation to collect acceleration responses. The stochastic subspace identification （SSI） method was adopted to calculate the structural modal parameters and obtain the out-of-plane vibration characteristics of the slab and frames. The results indicated that the wall-frame structure had a lower out-of-plane stiffness and greater in-plane stiffness due to the presence of stone walls. Due to poor identified damping ratio estimates from the SSI method, a method based on the variance upper bound was proposed to complement the existing variance lower bound method for estimating the modal damping ratio to address the significant damping variability obtained from different points and measurements. The feasibility of the proposed method was illustrated with the measured data from the floor slab of the structure. The variance lower and upper bound methods both provided consistent results compared to those from the traditional SSI method.
基金supported by the National Natural Science Foundation of China(No.52079133)CRSRI Open Research Program(Program SN:CKWV2019746/KY)+1 种基金the project of Key Laboratory of Water Grid Project and Regulation of Ministry of Water Resources(QTKS0034W23291)the Youth Innovation Promotion Association CAS.
文摘Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using a rubber-sand-concrete(RSC)as the aseismic material,is proposed.The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests.The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis,composite loss factor and damping ratio of the transfer function analysis,and total vibration level of octave spectrum analysis were discussed.The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear,and that the hollow damping layer had a better aseismic performance than the flat damping layer one.The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated.The effects of the peak ground acceleration(PGA)and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain(PEEQ)were discussed.The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance,with PGA in the range(0.2-1.2)g and tunnel overburden depth in the range of 0-300 m.
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the National Natural Science Foundation of China (Nos. 52388102, 52072317 and U2268210)the State Key Laboratory of Rail Transit Vehicle System (No. 2024RVL-T12)
文摘Hunting stability is an important performance criterion in railway vehicles.This study proposes an incorporation of a bio-inspired limb-like structure(LLS)-based nonlinear damping into the motor suspension system for traction units to improve the nonlinear critical speed and hunting stability of high-speed trains(HSTs).Initially,a vibration transmission analysis is conducted on a HST vehicle and a metro vehicle that suffered from hunting motion to explore the effect of different motor suspension systems from on-track tests.Subsequently,a simplified lateral dynamics model of an HST bogie is established to investigate the influence of the motor suspension on the bogie hunting behavior.The bifurcation analysis is applied to optimize the motor suspension parameters for high critical speed.Then,the nonlinear damping of the bio-inspired LLS,which has a positive correlation with the relative displacement,can further improve the modal damping of hunting motion and nonlinear critical speed compared with the linear motor suspension system.Furthermore,a comprehensive numerical model of a high-speed train,considering all nonlinearities,is established to investigate the influence of different types of motor suspension.The simulation results are well consistent with the theoretical analysis.The benefits of employing nonlinear damping of the bio-inspired LLS into the motor suspension of HSTs to enhance bogie hunting stability are thoroughly validated.
基金funded by the Austrian Federal Railways (ÖBB Infrastruktur AG) in the context of the research project ‘Ve Mo Diss’ (acronym)
文摘A realistic and economical dynamic assessment of railway bridges requires input parameters that correspond to reality.In this context,the applied damping properties of the structure have a decisive influence on the results in the prediction of resonance effects and further in the assessment of the compatibility between rolling stock and railway bridges.The standard prescribes damping factors depending on the type of structure and the span to be used in dynamic calculations.However,these factors can be regarded as very conservative values which do not represent reality.Thus,in situ measurements on the structure are often necessary to classify a bridge categorised as critical in prior dynamic calculations as non-critical.Regarding in situ tests,a measurement-based determination of the damping factor is inevitably accompanied by a scattering of the generated results due to the measurement method used and as a result of the individual scope of action of the test-evaluating person and this person’s interpretation of the measurement data.This paper presents novel evaluation methods and analysis tools for determining the damping factor based on measurements in the frequency and time domains,intending to reduce the scatter of the results and limit the scope of action of the person evaluating the test.The main aim is to provide simple and easy-to-use evaluation algorithms for practical applications without additional data transformations and to define clear principles of action for the data-based evaluation of realistic and high damping factors.Based on in situ tests on 15 existing railway bridges,the data-based procedure for determining the damping factor is explained,and the methods are compared in the time and frequency domains.It is shown that a clearly defined evaluation algorithm can significantly reduce the scattering of results.Furthermore,it is demonstrated that forced vibration excitation and evaluation in the frequency domain provide the best results in reliable,reproducible,and high damping factors.
文摘The methods of modifying dimension and shape of structure, or covering damping material are effective to reduce structure-borne noise, while these methods are based on the knowledge of qualitative and quantitative relationship between sound radiation and design parameters. In order to decrease the complexity of the problem, response surface method(RSM) was utilized to analyze and optimize the vibro-acoustic properties of the damping structure. A simple case was illustrated to demonstrate the capabilities of the developed procedure. A structure-born noise problem was approximated by a series of polynomials using RSM. Three main performances were considered, i.e. sound radiation power, first order modal frequency and total mass. Consequently, the response surface model not only gives the direction of design modification, it also leads to an optimal design of complex systems.
文摘The stress strain curves of two CuZnAl shape memory alloys which have the martensitic transformation temperatures of 50 ℃ and -10 ℃ respectively, were measured by using electronic material tester after treated by different heat-treatment conditions. The results show that the area enclosed by hysteresis loop of the CuZnAl shape memory alloy in martensitic state is much larger than that of the alloy in austenitic state with super-elasticity at room temperature. Therefore, the former has better vibration attenuation effect. After being oil-quenched, water-quenched, and step-quenched, the CuZnAl alloy takes on more stable shape memory effect,better super-plasticity and superelasticity (pseudoelasticity). A CuZnAl shape memory alloy damper was designed, produced and installed to a 2-layer frame structure. In addition, the vibration experiments were made by dynamic data collecting analysis meter. The velocity of vibration attenuation of frame structure with CuZnAl shape memory alloy damper is much faster than that without it. And with the help of CuZnAl shape memory alloy damper, the attenuation period reduces to 1/10 of the original.
文摘This study examines the roles of soil-structure interaction （SSI）, higher modes, and damping in a base-isolated structure built on multiple layers of soil overlying a half space. Closed-form solutions for the entire system, including a superstructure, seismic isolator, and numerous soil layers overlying a half-space, were obtained. The formulations obtained in this study simply in terms of well-known frequencies and mechanical impedance ratios can explicitly interpret the dynamic behavior of a base-isolated structure interacting with multiple soil layers overlying a half-space. The key factors influencing the performance of the isolation system are the damping ratio of the isolator and the ratio of the natural frequency of the fixed-base structure to that of the isolated structure by assuming that the superstructure moves as a rigid body. This study reveals that higher damping in the base isolator is unfavorable to higher mode responses that usually dominate the responses of the superstructure and that the damping mechanism plays an important role in transmitting energy in addition to absorbing energy. It is also concluded that it is possible to design a soft soil layer as an isolation system for isolating vibration energy.
基金Science and Technology Foundation of China Academy of Engineering Physics (20060321)
文摘The damping material optimal placement for the structure with damping layer is studied based on evolutionary structural optimization (ESO) to maximize modal loss factors. A mathematical model is constructed with the objective function defined as the maximum of modal loss factors of the structure and design constraints function defined as volume fraction of damping material. The optimal placement is found. Several examples are presented for verification. The results demonstrate that the method based on ESO is effective in solving the topology optimization of the structure with unconstrained damping layer and constrained damping layer. This optimization method suits for free and constrained damping structures.
基金Project(NCET-11-0554)supported by the Program for New Century Excellent Talents in University,ChinaProject(2011BAE22B04)supported by the National Key Technology R&D Program,ChinaProject(51271206)supported by the National Natural Science Foundation of China
文摘Three kinds of different phases of Mg-xLi-1Al alloys with x=5 （full α LA51）, 9 （dual-phase LA91）, and 14 （rich-βLA141） were prepared by vacuum melting method. Their microstructure and damping capacities were investigated by optical microscopy, X-ray diffractometry, and dynamic mechanical analysis. The results show that the addition of Li changes the crystal structure of the alloys and causes new damping mechanisms to emerge. And the appearance of BCC structure makes the damping performance improved remarkably. The lower the elastic modulus is, the smaller the strain is and even the slower the acceleration is. The dual-phase alloy shows a better damping capacity while the temperature changes. Furthermore, all three alloys have two significant peaks：P1 caused by the movement of dislocations on the basal planes and P2 caused by the sliding of grain boundaries.
基金National Natural Science Foundation of China Under Grant No.40072088
文摘A method to calculate the stationary random response of a non-classically damped structure is proposed that features clearly-defined physical meaning and simple expression. The method is developed in the frequency domain. The expression of the proposed method consists of three terms, i.e., modal velocity response, modal displacement response, and coupled (between modal velocity and modal displacement response). Numerical results from the parametric study and three example structures reveal that the modal velocity response term and the coupled term are important to structural response estimates only for a dynamic system with a tuned mass damper. In typical cases, the modal displacement term can provide response estimates with satisfactory accuracy by itself, so that the modal velocity term and coupled term may be ignored without loss of accuracy. This is used to simplify the response computation of non-classically damped structures. For the white noise excitation, three modal correlation coefficients in closed form are derived. To consider the modal velocity response term and the coupled term, a simplified approximation based on white noise excitation is developed for the case when the modal velocity response is important to the structural responses. Numerical results show that the approximate expression based on white noise excitation can provide structural responses with satisfactory accuracy.
基金Sponsored by the National 863 Project of China (Grant No. 863 -2 -416)
文摘By analyzing the correlation between modal calculations and modal experiments of a typical supporter, an effective finite element analysis( FEA)model of the actual aerospace supporter is created. According to the analysis of constrained viscoelastic damping, the strategies of PVC have been worked out, and the correlation between modal calculations and modal experiments of the supporter has also been computed, and then, an experiment has been designed based on the calculation results. The results of experiments verify that the PVC strategy can effectively suppress vibration.
