The behavior of building materials in constructions of civil structures is influenced by the surrounding moisture and it is a crucial for intensively examined field of the construction physics. Most standard building ...The behavior of building materials in constructions of civil structures is influenced by the surrounding moisture and it is a crucial for intensively examined field of the construction physics. Most standard building materials are characterized by a porous structure, which results in the ability to receive water in a liquid as well as gaseous form in the inner pores. The water fills the storage space of pores under certain conditions; it is transported and transferred back to the surroundings. Many technical studies show that the moisture monitoring is prevailingly based on experiments. Previous calculating methods introduced, e.g., by Glaser, which became the basis for the standard calculations in many European countries in the 1960s, are not always sufficient with respect to the demands of the civil structures. The moisture influences thermo-insulating properties of the material. By a change of the thermo insulation properties of the construction also the thermal and diffusion scheme of the construction is changed and its thermal resistance is decreasing. Faults in the thermo-technical projects occur when thermal conductivity coefficient L values for material in a dry state are substituted.The aim of the research is to determine the capillary conductivity coefficient as a characteristic material moisture parameter of the building materials by the means of a non-destructive method using the experimentally assembled apparatus developed at the Department of Civil Engineering, Brno University of Technology. Keywords： Capillary conductivity coefficient, moisture transfer, EMWR （electromagnetic microwave radiation）, diffusion展开更多
In this article, transverse free vibrations of axially moving nanobeams subjected to axial tension are studied based on nonlocal stress elasticity theory. A new higher-order differential equation of motion is derived ...In this article, transverse free vibrations of axially moving nanobeams subjected to axial tension are studied based on nonlocal stress elasticity theory. A new higher-order differential equation of motion is derived from the variational principle with corresponding higher-order, non-classical boundary conditions. Two supporting conditions are investigated, i.e. simple supports and clamped supports. Effects of nonlocal nanoscale, dimensionless axial velocity, density and axial tension on natural frequencies are presented and discussed through numerical examples. It is found that these factors have great influence on the dynamic behaviour of an axially moving nanobeam. In particular, the nonlocal effect tends to induce higher vibration frequencies as compared to the results obtained from classical vibration theory. Analytical solutions for critical velocity of these nanobeams when the frequency vanishes are also derived and the influences of nonlocal nanoscale and axial tension on the critical velocity are discussed.展开更多
An elasto-plastie impact model based on the p-version finite element method is presented for the collision protection of ocean and offshore structures. The impact force and responses of the impactor-absorber-structure...An elasto-plastie impact model based on the p-version finite element method is presented for the collision protection of ocean and offshore structures. The impact force and responses of the impactor-absorber-structure system can be predicted efficiently and automatically. A cost-effective Cellular Reinforced Concrete Absorber （CRCA） is designed to smooth the impact force and absorb the impact energy. Quasi-static tests show that the concrete absorber has an excellent energy absorbing characteristic. The impact experiment of a scaled offshore oil-piping frame with the proposed concrete absorber is carried out. The simulation results of the elasto-plastie model and the p-version finite element method are in good agreement with the experimental ones. Owing to the plastic deformation of the absorber, the impact force during the impact and responses of the structure are considerably reduced. Further, the proposed impact model and the concrete absorber are applied to the design of collision protection of the sheet-pile groin on the Qiantang River used to weaken the famous Qiantang bore.展开更多
This paper proposes an improved cellular automaton model to describe the urban traffic flow with the consideration of traffic light and driving behaviour effects. Based on the model, the characteristics of the urban t...This paper proposes an improved cellular automaton model to describe the urban traffic flow with the consideration of traffic light and driving behaviour effects. Based on the model, the characteristics of the urban traffic flow on a single- lane road are investigated under three different control strategies, i.e., the synchronized, the green wave and the random strategies. The fundamental diagrams and time-space patterns of the traffic flows are provided for these strategies respectively. It finds that the dynamical transition to the congested flow appears when the vehicle density is higher than a critical level. The saturated flow is less dependent on the cycle time and the strategies of the traffic light control, while the critical vehicle density varies with the cycle time and the strategies. Simulated results indicate that the green wave strategy is proven to be the most effective one among the above three control strategies.展开更多
In this paper, the evaluation of stress intensity factor of plane crack problems for orthotropic plate of equal-parameter is investigated using a fractal two-level finite element method （F2LFEM）. The general solutio...In this paper, the evaluation of stress intensity factor of plane crack problems for orthotropic plate of equal-parameter is investigated using a fractal two-level finite element method （F2LFEM）. The general solution of an orthotropic crack problem is obtained by assimilating the problem with isotropic crack problem, and is employed as the global interpolation function in F2LFEM. In the neighborhood of crack tip of the crack plate, the fractal geometry concept is introduced to achieve the similar meshes having similarity ratio less than one and generate an infinitesimal mesh so that the relationship between the stiffness matrices of two adjacent layers is equal. A large number of degrees of freedom around the crack tip are transformed to a small set of generalized coordinates. Numerical examples show that this method is efficient and accurate in evaluating the stress intensity factor （SIF）.展开更多
This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams： （i） why does the presence of increasing nonlocal effects induce reduced nanostructur...This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams： （i） why does the presence of increasing nonlocal effects induce reduced nanostructural stiffness in many, but not consistently for all, cases of study, i.e., increasing static deflection, decreasing natural frequency and decreasing buckling load, although physical intuition according to the nonlocal elasticity field theory first established by Eringen tells otherwise？ （ii） the intriguing conclusion that nanoscale effects are missing in the solutions in many exemplary cases of study, e.g., bending deflection of a cantilever nanobeam with a point load at its tip; and （iii） the non-existence of additional higher-order boundary conditions for a higher-order governing differential equation. Applying the nonlocal elasticity field theory in nanomechanics and an exact variational principal approach, we derive the new equilibrium conditions, do- main governing differential equation and boundary conditions for bending of nanobeams. These equations and conditions involve essential higher-order differential terms which are opposite in sign with respect to the previously studies in the statics and dynamics of nonlocal nano-structures. The difference in higher-order terms results in reverse trends of nanoscale effects with respect to the conclusion of this paper. Effectively, this paper reports new equilibrium conditions, governing differential equation and boundary condi- tions and the true basic static responses for bending of nanobeams. It is also concluded that the widely accepted equilibrium conditions of nonlocal nanostructures are in fact not in equilibrium, but they can be made perfect should the nonlocal bending moment be replaced by an effective nonlocal bending moment. These conclusions are substantiated, in a general sense, by other approaches in nanostructural models such as strain gradient theory, modified couple stress models and experiments.展开更多
A new two dimensional coupled electromechanical model for a thick, laminated beam with piezoelectric and isotropic lamina subjected to static external electric loading is developed. The model combined the first order ...A new two dimensional coupled electromechanical model for a thick, laminated beam with piezoelectric and isotropic lamina subjected to static external electric loading is developed. The model combined the first order shear deformation theory for the relatively thick elastic core and linear piezoelectric theory for the piezoelectric lamina. The actuation response is induced through the application of external electric voltage. Rayleigh-Ritz method is adopted to model the displacement and potential fields of the beam and governing equations were finally derived from the variational energy principle. The model allows the piezoelectric lamina to be formulated via a two-dimensional model because of the strong electro-mechanical coupling and the presence of a two-dimensional electric field. Numerical examples of piezoelectric laminated beam are presented. It is shown in this paper that a one-dimensional model for the piezoelectric beam-like layer is inadequate.展开更多
The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration...The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions:simple supports,clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma-tion and vibration modes are derived. Through numerical examples,effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.展开更多
The first-order approximation coupling （FOAC） model was proposed recently for dynamics and control of flexible hub-beam systems. This model may deal with system dynamics for both low and high rotation speed, while t...The first-order approximation coupling （FOAC） model was proposed recently for dynamics and control of flexible hub-beam systems. This model may deal with system dynamics for both low and high rotation speed, while the classical zeroth-order approximation coupling （ZOAC） model is only available for low rotation speed. This paper assumes the FOAC model to present experimental study of active positioning control of a flexible hub-beam system. Linearization and nonlinear control strategies are both considered. An experiment system based on a DSP TMS320F2812 board is introduced. The difference between linearization and nonlinear control strategies are studied both numerically and experimentally. Simulation and experimental results indicate that, linearized controller can make the system reach an expected position with suppressed vibration of flexible beam, but the time taken to position is longer than expected, whereas nonlinear controller works well with precise positioning, suppression of vibration and time control.展开更多
This paper proposes a new traffic model to describe traffic flow with slope under consideration of the gravity effect.Based on the model,stability analysis is conducted and a numerical simulation is performed to explo...This paper proposes a new traffic model to describe traffic flow with slope under consideration of the gravity effect.Based on the model,stability analysis is conducted and a numerical simulation is performed to explore the characteristics of the traffic flow with slope.The result shows that the perturbation of the system is an inherent one,which is induced by the slope.In addition,the hysteresis loop is represented through plotting the figure of velocity against headway and highly depends on the slope angle. The kinematic wave at high density is also obtained through reproducing the phenomenon of stop-and-go traffic,which is significant to explore the phase transition of traffic flow and the evolution of traffic congestion.展开更多
A linear semi-continuum model with discrete atomic layers in the thickness direction was developed to investigate the bending behaviors of ultra-thin beams with nanoscale thickness.The theoretical results show that th...A linear semi-continuum model with discrete atomic layers in the thickness direction was developed to investigate the bending behaviors of ultra-thin beams with nanoscale thickness.The theoretical results show that the deflection of an ultra-thin beam may be enhanced or reduced due to different relaxation coefficients.If the relaxation coefficient is greater/less than one,the deflection of micro/nano-scale structures is enhanced/reduced in comparison with macro-scale structures.So,two opposite types of size-dependent behaviors are observed and they are mainly caused by the relaxation coefficients.Comparisons with the classical continuum model,exact nonlocal stress model and finite element model （FEM） verify the validity of the present semi-continuum model.In particular,an explanation is proposed in the debate whether the bending stiffness of a micro/nano-scale beam should be greater or weaker as compared with the macro-scale structures.The characteristics of bending stiffness are proved to be associated with the relaxation coefficients.展开更多
Semi-analytical elasticity solutions for bending of angle-ply laminates in cylindrical bending are presented using the state-space-based differential quadrature method (SSDQM). Partial differential state equation is d...Semi-analytical elasticity solutions for bending of angle-ply laminates in cylindrical bending are presented using the state-space-based differential quadrature method (SSDQM). Partial differential state equation is derived from the basic equations of elasticity based on the state space concept. Then, the differential quadrature (DQ) technique is introduced to discretize the longitu- dinal domain of the plate so that a series of ordinary differential state equations are obtained at the discrete points. Meanwhile, the edge constrained conditions are handled directly using the stress and displacement components without the Saint-Venant principle. The thickness domain is solved analytically based on the state space formalism along with the continuity conditions at interfaces. The present method is validated by comparing the results to the exact solutions of Pagano’s problem. Numerical results for fully clamped thick laminates are presented, and the influences of ply angle on stress distributions are discussed.展开更多
Based on the optimal velocity models, an extended model is proposed, in which multi-veloclty-dllterence aheacl is taken into consideration. The damping effect of the multi-velocity-difference ahead has been investigat...Based on the optimal velocity models, an extended model is proposed, in which multi-veloclty-dllterence aheacl is taken into consideration. The damping effect of the multi-velocity-difference ahead has been investigated by means of analytical and numerical methods. Results indicate that the multi-velocity-difference leads to the enhancement of stability of traffic flow, suppression of the emergence of traffic jamming, and reduction of the energy consumption.展开更多
The application of the saddlepoint approximation to reliability analysis of dynamic systems is investigated. The failure event in reliability problems is formulated as the exceedance of a single performance variable o...The application of the saddlepoint approximation to reliability analysis of dynamic systems is investigated. The failure event in reliability problems is formulated as the exceedance of a single performance variable over a prescribed threshold level. The saddlepoint approximation technique provides a choice to estimate the cumulative distribution function （CDF） of the performance variable. The failure probability is obtained as the value of the complement CDF at a specified threshold. The method requires computing the saddlepoint from a simple algebraic equation that depends on the cumulant generating function （CGF） of the performance variable. A method for calculating the saddlepoint using random samples of the performance variable is presented. The applicable region of the saddlepoint approximation is discussed in detail. A 10-story shear building model with white noise excitation illustrates the accuracy and efficiency of the proposed methodology.展开更多
Exact solutions in form of elementary functions were derived for the stress and electric displacement intensity factors of a circular crack in a transversely isotropic piezoelectric space interacting with various stre...Exact solutions in form of elementary functions were derived for the stress and electric displacement intensity factors of a circular crack in a transversely isotropic piezoelectric space interacting with various stress and charge sources： force dipoles, electric dipoles, moments, force dilatation and rotation. The circular crack includes penny-shaped crack and external circular crack and the locations and orientations of these resultant sources with respect to the crack are arbitrary. Such stress and charge sources may model defects like vacancies, foreign particles, and dislocations. Numerical results are presented at last.展开更多
This paper presents a symplectic method for two-dimensional transversely isotropic piezoelectric media with the aid of Hamiltonian system. A symplectic system is established directly by introducing dual variables and ...This paper presents a symplectic method for two-dimensional transversely isotropic piezoelectric media with the aid of Hamiltonian system. A symplectic system is established directly by introducing dual variables and a complete space of eigensolutions is obtained. The solutions of the problem can be expressed by eigensolutions. Some solutions, which are local and are neglected usually by Saint Venant principle, are shown. Curves of non-zero-eigenvalues and their eigensolutions are given by the numerical results.展开更多
Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive （bentonite–s...Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive （bentonite–sand （B–S） mixture） and non-expansive （kaolin） soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties （swelling pressure, expansion indices, shear strength （soil cohesion） and soil suction） for the small soil samples. Large-scale model was also used to show the effect of water content change on different relations （swelling and suction with elapsed time）. The study reveals that the initial soil conditions （water content and dry unit weight） affect the soil cohesion, suction and swelling, where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content. The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform. The settlement observed in B–S mixture is higher than that in kaolin due to the effect of higher swelling observed in B–S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil. The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen. The tensiometer reading at first of the saturation process is lower than that at later period of saturation （for soil sample B–S3, the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage, while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa）.展开更多
This paper proposes a statistical method for damage detection based on the finite element （FE） model reduction technique that utilizes measured modal data with a limited number of sensors. A deterministic damage det...This paper proposes a statistical method for damage detection based on the finite element （FE） model reduction technique that utilizes measured modal data with a limited number of sensors. A deterministic damage detection process is formulated based on the model reduction technique. The probabilistie process is integrated into the deterministic damage detection process using a perturbation technique, resulting in a statistical structural damage detection method. This is achieved by deriving the first- and second-order partial derivatives of uncertain parameters, such as elasticity of the damaged member, with respect to the measurement noise, which allows expectation and covariance matrix of the uncertain parameters to be calculated. Besides the theoretical development, this paper reports numerical verification of the proposed method using a portal frame example and Monte Carlo simulation.展开更多
The topological bifurcation diagrams and the coefficients of bifurcation equation were obtained by C_L method.According to obtained bifurcation diagrams and combining control theory,the method of robust control of per...The topological bifurcation diagrams and the coefficients of bifurcation equation were obtained by C_L method.According to obtained bifurcation diagrams and combining control theory,the method of robust control of periodic bifurcation was presented,which differs from generic methods of bifurcation control.It can make the existing motion pattern into the goal motion pattern.Because the method does not make strict requirement about parametric values of the controller,it is convenient to design and make it.Numerical simulations verify validity of the method.展开更多
When using H_∞ techniques to design decentralized controllers for large systems, the whole system is divided into subsystems, which are analysed using H_∞ control theory before being recombined. An analogy was estab...When using H_∞ techniques to design decentralized controllers for large systems, the whole system is divided into subsystems, which are analysed using H_∞ control theory before being recombined. An analogy was established with substructural analysis in structural mechanics, in which H_∞ decentralized control theory corresponds to substructural modal synthesis theory so that the optimal H_∞ norm of the whole system corresponds to the fundamental vibration frequency of the whole structure. Hence, modal synthesis methodology and the extended Wittrick_Williams algorithm were transplanted from structural mechanics to compute the optimal H_∞ norm of the control system. The orthogonality and the expansion theorem of eigenfunctions of the subsystems H_∞ control are presented in part (Ⅰ) of the paper. The modal synthesis method for computation of the optimal H_∞ norm of decentralized control systems and numerical examples are presented in part (Ⅱ).展开更多
文摘The behavior of building materials in constructions of civil structures is influenced by the surrounding moisture and it is a crucial for intensively examined field of the construction physics. Most standard building materials are characterized by a porous structure, which results in the ability to receive water in a liquid as well as gaseous form in the inner pores. The water fills the storage space of pores under certain conditions; it is transported and transferred back to the surroundings. Many technical studies show that the moisture monitoring is prevailingly based on experiments. Previous calculating methods introduced, e.g., by Glaser, which became the basis for the standard calculations in many European countries in the 1960s, are not always sufficient with respect to the demands of the civil structures. The moisture influences thermo-insulating properties of the material. By a change of the thermo insulation properties of the construction also the thermal and diffusion scheme of the construction is changed and its thermal resistance is decreasing. Faults in the thermo-technical projects occur when thermal conductivity coefficient L values for material in a dry state are substituted.The aim of the research is to determine the capillary conductivity coefficient as a characteristic material moisture parameter of the building materials by the means of a non-destructive method using the experimentally assembled apparatus developed at the Department of Civil Engineering, Brno University of Technology. Keywords： Capillary conductivity coefficient, moisture transfer, EMWR （electromagnetic microwave radiation）, diffusion
基金supported by a collaboration scheme from University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Institute and by City University of Hong Kong(7002472 (BC))
文摘In this article, transverse free vibrations of axially moving nanobeams subjected to axial tension are studied based on nonlocal stress elasticity theory. A new higher-order differential equation of motion is derived from the variational principle with corresponding higher-order, non-classical boundary conditions. Two supporting conditions are investigated, i.e. simple supports and clamped supports. Effects of nonlocal nanoscale, dimensionless axial velocity, density and axial tension on natural frequencies are presented and discussed through numerical examples. It is found that these factors have great influence on the dynamic behaviour of an axially moving nanobeam. In particular, the nonlocal effect tends to induce higher vibration frequencies as compared to the results obtained from classical vibration theory. Analytical solutions for critical velocity of these nanobeams when the frequency vanishes are also derived and the influences of nonlocal nanoscale and axial tension on the critical velocity are discussed.
文摘An elasto-plastie impact model based on the p-version finite element method is presented for the collision protection of ocean and offshore structures. The impact force and responses of the impactor-absorber-structure system can be predicted efficiently and automatically. A cost-effective Cellular Reinforced Concrete Absorber （CRCA） is designed to smooth the impact force and absorb the impact energy. Quasi-static tests show that the concrete absorber has an excellent energy absorbing characteristic. The impact experiment of a scaled offshore oil-piping frame with the proposed concrete absorber is carried out. The simulation results of the elasto-plastie model and the p-version finite element method are in good agreement with the experimental ones. Owing to the plastic deformation of the absorber, the impact force during the impact and responses of the structure are considerably reduced. Further, the proposed impact model and the concrete absorber are applied to the design of collision protection of the sheet-pile groin on the Qiantang River used to weaken the famous Qiantang bore.
基金supported by the Strategic Research Grants from City University of Hong Kong [Project No. CityU-SRG 7002370]the National Natural Science Foundation of China (Grant No. 10972135)+1 种基金Science Foundation of Shanghai Maritime University(Grant No. 20110046)the Science Foundation of Shanghai Science Commission (Grant Nos. 09DZ2250400 and 09530708200)
文摘This paper proposes an improved cellular automaton model to describe the urban traffic flow with the consideration of traffic light and driving behaviour effects. Based on the model, the characteristics of the urban traffic flow on a single- lane road are investigated under three different control strategies, i.e., the synchronized, the green wave and the random strategies. The fundamental diagrams and time-space patterns of the traffic flows are provided for these strategies respectively. It finds that the dynamical transition to the congested flow appears when the vehicle density is higher than a critical level. The saturated flow is less dependent on the cycle time and the strategies of the traffic light control, while the critical vehicle density varies with the cycle time and the strategies. Simulated results indicate that the green wave strategy is proven to be the most effective one among the above three control strategies.
文摘In this paper, the evaluation of stress intensity factor of plane crack problems for orthotropic plate of equal-parameter is investigated using a fractal two-level finite element method （F2LFEM）. The general solution of an orthotropic crack problem is obtained by assimilating the problem with isotropic crack problem, and is employed as the global interpolation function in F2LFEM. In the neighborhood of crack tip of the crack plate, the fractal geometry concept is introduced to achieve the similar meshes having similarity ratio less than one and generate an infinitesimal mesh so that the relationship between the stiffness matrices of two adjacent layers is equal. A large number of degrees of freedom around the crack tip are transformed to a small set of generalized coordinates. Numerical examples show that this method is efficient and accurate in evaluating the stress intensity factor （SIF）.
基金supported by a grant from Research Grants Council of the Hong Kong Special Administrative Region (No. CityU 117406)
文摘This paper has successfully addressed three critical but overlooked issues in nonlocal elastic stress field theory for nanobeams： （i） why does the presence of increasing nonlocal effects induce reduced nanostructural stiffness in many, but not consistently for all, cases of study, i.e., increasing static deflection, decreasing natural frequency and decreasing buckling load, although physical intuition according to the nonlocal elasticity field theory first established by Eringen tells otherwise？ （ii） the intriguing conclusion that nanoscale effects are missing in the solutions in many exemplary cases of study, e.g., bending deflection of a cantilever nanobeam with a point load at its tip; and （iii） the non-existence of additional higher-order boundary conditions for a higher-order governing differential equation. Applying the nonlocal elasticity field theory in nanomechanics and an exact variational principal approach, we derive the new equilibrium conditions, do- main governing differential equation and boundary conditions for bending of nanobeams. These equations and conditions involve essential higher-order differential terms which are opposite in sign with respect to the previously studies in the statics and dynamics of nonlocal nano-structures. The difference in higher-order terms results in reverse trends of nanoscale effects with respect to the conclusion of this paper. Effectively, this paper reports new equilibrium conditions, governing differential equation and boundary condi- tions and the true basic static responses for bending of nanobeams. It is also concluded that the widely accepted equilibrium conditions of nonlocal nanostructures are in fact not in equilibrium, but they can be made perfect should the nonlocal bending moment be replaced by an effective nonlocal bending moment. These conclusions are substantiated, in a general sense, by other approaches in nanostructural models such as strain gradient theory, modified couple stress models and experiments.
基金Project (No. 7001687 (BC)) supported by City University of HongKong, China
文摘A new two dimensional coupled electromechanical model for a thick, laminated beam with piezoelectric and isotropic lamina subjected to static external electric loading is developed. The model combined the first order shear deformation theory for the relatively thick elastic core and linear piezoelectric theory for the piezoelectric lamina. The actuation response is induced through the application of external electric voltage. Rayleigh-Ritz method is adopted to model the displacement and potential fields of the beam and governing equations were finally derived from the variational energy principle. The model allows the piezoelectric lamina to be formulated via a two-dimensional model because of the strong electro-mechanical coupling and the presence of a two-dimensional electric field. Numerical examples of piezoelectric laminated beam are presented. It is shown in this paper that a one-dimensional model for the piezoelectric beam-like layer is inadequate.
基金supported by the Collaboration Scheme from University of Science and Technology of China and City University of Hong Kong Joint Advanced Research Institute, and City University of Hong Kong (No. 7002357 (BC))
文摘The transverse free vibration of nanobeams subjected to an initial axial tension based on nonlocal stress theory is presented. It considers the effects of nonlocal stress field on the natural frequencies and vibration modes. The effects of a small scale parameter at molecular level unavailable in classical macro-beams are investigated for three different types of boundary conditions:simple supports,clamped supports and elastically-constrained supports. Analytical solutions for transverse deforma-tion and vibration modes are derived. Through numerical examples,effects of the dimensionless nanoscale parameter and pre-tension on natural frequencies are presented and discussed.
基金supported by the National Natural Science Foundation of China(10772112 and 10472065)the Key Project of Ministry of Education of China(107043)+2 种基金the Key Scientific Project of Shanghai Municipal Education Commission(09ZZ 17)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20070248032)the Research Project of State Key Laboratory of Ocean Engineering of China(GKZD010807)
文摘The first-order approximation coupling （FOAC） model was proposed recently for dynamics and control of flexible hub-beam systems. This model may deal with system dynamics for both low and high rotation speed, while the classical zeroth-order approximation coupling （ZOAC） model is only available for low rotation speed. This paper assumes the FOAC model to present experimental study of active positioning control of a flexible hub-beam system. Linearization and nonlinear control strategies are both considered. An experiment system based on a DSP TMS320F2812 board is introduced. The difference between linearization and nonlinear control strategies are studied both numerically and experimentally. Simulation and experimental results indicate that, linearized controller can make the system reach an expected position with suppressed vibration of flexible beam, but the time taken to position is longer than expected, whereas nonlinear controller works well with precise positioning, suppression of vibration and time control.
基金Project supported partially by the Strategic Research Grants from City University of Hong Kong (Grant Nos SRG 7002226(BC)and SRG 7002370(BC))the National Natural Science Foundation of China (Grant Nos 10662002,10672098 and 10532020)
文摘This paper proposes a new traffic model to describe traffic flow with slope under consideration of the gravity effect.Based on the model,stability analysis is conducted and a numerical simulation is performed to explore the characteristics of the traffic flow with slope.The result shows that the perturbation of the system is an inherent one,which is induced by the slope.In addition,the hysteresis loop is represented through plotting the figure of velocity against headway and highly depends on the slope angle. The kinematic wave at high density is also obtained through reproducing the phenomenon of stop-and-go traffic,which is significant to explore the phase transition of traffic flow and the evolution of traffic congestion.
基金supported by a collaboration scheme from University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Institute,City University of HongKong (7002472 (BC))the National Natural Science Founda-tion of China (10932011)
文摘A linear semi-continuum model with discrete atomic layers in the thickness direction was developed to investigate the bending behaviors of ultra-thin beams with nanoscale thickness.The theoretical results show that the deflection of an ultra-thin beam may be enhanced or reduced due to different relaxation coefficients.If the relaxation coefficient is greater/less than one,the deflection of micro/nano-scale structures is enhanced/reduced in comparison with macro-scale structures.So,two opposite types of size-dependent behaviors are observed and they are mainly caused by the relaxation coefficients.Comparisons with the classical continuum model,exact nonlocal stress model and finite element model （FEM） verify the validity of the present semi-continuum model.In particular,an explanation is proposed in the debate whether the bending stiffness of a micro/nano-scale beam should be greater or weaker as compared with the macro-scale structures.The characteristics of bending stiffness are proved to be associated with the relaxation coefficients.
基金Project supported by the National Natural Science Foundation of China (No. 10432030)the China Postdoctoral Science Foundation (No. 20060401071)the Program for New Century Excellent Talent in University of China (No. NCET-05-0510)
文摘Semi-analytical elasticity solutions for bending of angle-ply laminates in cylindrical bending are presented using the state-space-based differential quadrature method (SSDQM). Partial differential state equation is derived from the basic equations of elasticity based on the state space concept. Then, the differential quadrature (DQ) technique is introduced to discretize the longitu- dinal domain of the plate so that a series of ordinary differential state equations are obtained at the discrete points. Meanwhile, the edge constrained conditions are handled directly using the stress and displacement components without the Saint-Venant principle. The thickness domain is solved analytically based on the state space formalism along with the continuity conditions at interfaces. The present method is validated by comparing the results to the exact solutions of Pagano’s problem. Numerical results for fully clamped thick laminates are presented, and the influences of ply angle on stress distributions are discussed.
基金Project supported by the National Basic Research Program of China (Grant No 2006CB705500)the National Natural Science Foundation of China (Grant Nos 10662002 and 10532060)+1 种基金the Special Foundation for the New Century Talents Program of Guangxi Zhuang Autonomous Region, China (Grant No 2005205)the Research Grants from City University of Hong Kong (Grant No SRG7002226(BC))
文摘Based on the optimal velocity models, an extended model is proposed, in which multi-veloclty-dllterence aheacl is taken into consideration. The damping effect of the multi-velocity-difference ahead has been investigated by means of analytical and numerical methods. Results indicate that the multi-velocity-difference leads to the enhancement of stability of traffic flow, suppression of the emergence of traffic jamming, and reduction of the energy consumption.
基金Research Committee of University of Macao Under Grant No. G074/05-06S/YKV/FST UMAC.
文摘The application of the saddlepoint approximation to reliability analysis of dynamic systems is investigated. The failure event in reliability problems is formulated as the exceedance of a single performance variable over a prescribed threshold level. The saddlepoint approximation technique provides a choice to estimate the cumulative distribution function （CDF） of the performance variable. The failure probability is obtained as the value of the complement CDF at a specified threshold. The method requires computing the saddlepoint from a simple algebraic equation that depends on the cumulant generating function （CGF） of the performance variable. A method for calculating the saddlepoint using random samples of the performance variable is presented. The applicable region of the saddlepoint approximation is discussed in detail. A 10-story shear building model with white noise excitation illustrates the accuracy and efficiency of the proposed methodology.
基金Project supported by the National Natural Science Foundation of China (No.10472102)Special Foundation of City University of HongKong (No.9610022)Outstanding Young Teacher Foundation of Hunan Province (No.521105236)the Yu-Ying Foundation of Hunan University (No.531103011110)
文摘Exact solutions in form of elementary functions were derived for the stress and electric displacement intensity factors of a circular crack in a transversely isotropic piezoelectric space interacting with various stress and charge sources： force dipoles, electric dipoles, moments, force dilatation and rotation. The circular crack includes penny-shaped crack and external circular crack and the locations and orientations of these resultant sources with respect to the crack are arbitrary. Such stress and charge sources may model defects like vacancies, foreign particles, and dislocations. Numerical results are presented at last.
基金Project (Nos. 19902014 and 10272024) supported by the NationalNatural Science Foundation of China
文摘This paper presents a symplectic method for two-dimensional transversely isotropic piezoelectric media with the aid of Hamiltonian system. A symplectic system is established directly by introducing dual variables and a complete space of eigensolutions is obtained. The solutions of the problem can be expressed by eigensolutions. Some solutions, which are local and are neglected usually by Saint Venant principle, are shown. Curves of non-zero-eigenvalues and their eigensolutions are given by the numerical results.
文摘Limited studies dealt with the expansive unsaturated soils in the case of large-scale model close to the field conditions and therefore, there is much more room for improvement. In this study, expansive （bentonite–sand （B–S） mixture） and non-expansive （kaolin） soils were tested in different water contents and dry unit weights chosen from the compaction curve to examine the effect of water content change on soil properties （swelling pressure, expansion indices, shear strength （soil cohesion） and soil suction） for the small soil samples. Large-scale model was also used to show the effect of water content change on different relations （swelling and suction with elapsed time）. The study reveals that the initial soil conditions （water content and dry unit weight） affect the soil cohesion, suction and swelling, where all these parameters slightly decrease with the increase in soil water content especially on the wet side of optimum water content. The settlement of each soil at failure increases with the increase in soil degrees of saturation since the matric suction reduces the soil ability to deform. The settlement observed in B–S mixture is higher than that in kaolin due to the effect of higher swelling observed in B–S mixture and the huge amount of water absorbed which transformed the soil to highly compressible soil. The matric suction seems to decrease with elapsed time from top to bottom of tensiometers due to the effect of water flowing from top of the specimen. The tensiometer reading at first of the saturation process is lower than that at later period of saturation （for soil sample B–S3, the tensiometer #1 took 3 d to drop from 93 kPa to 80 kPa at early stage, while the same tensiometer took 2 d to drop from 60 kPa to 20 kPa）.
基金supported by the Strategic Research Grant of City University of Hong Kong (No.7001970)
文摘This paper proposes a statistical method for damage detection based on the finite element （FE） model reduction technique that utilizes measured modal data with a limited number of sensors. A deterministic damage detection process is formulated based on the model reduction technique. The probabilistie process is integrated into the deterministic damage detection process using a perturbation technique, resulting in a statistical structural damage detection method. This is achieved by deriving the first- and second-order partial derivatives of uncertain parameters, such as elasticity of the damaged member, with respect to the measurement noise, which allows expectation and covariance matrix of the uncertain parameters to be calculated. Besides the theoretical development, this paper reports numerical verification of the proposed method using a portal frame example and Monte Carlo simulation.
文摘The topological bifurcation diagrams and the coefficients of bifurcation equation were obtained by C_L method.According to obtained bifurcation diagrams and combining control theory,the method of robust control of periodic bifurcation was presented,which differs from generic methods of bifurcation control.It can make the existing motion pattern into the goal motion pattern.Because the method does not make strict requirement about parametric values of the controller,it is convenient to design and make it.Numerical simulations verify validity of the method.
文摘When using H_∞ techniques to design decentralized controllers for large systems, the whole system is divided into subsystems, which are analysed using H_∞ control theory before being recombined. An analogy was established with substructural analysis in structural mechanics, in which H_∞ decentralized control theory corresponds to substructural modal synthesis theory so that the optimal H_∞ norm of the whole system corresponds to the fundamental vibration frequency of the whole structure. Hence, modal synthesis methodology and the extended Wittrick_Williams algorithm were transplanted from structural mechanics to compute the optimal H_∞ norm of the control system. The orthogonality and the expansion theorem of eigenfunctions of the subsystems H_∞ control are presented in part (Ⅰ) of the paper. The modal synthesis method for computation of the optimal H_∞ norm of decentralized control systems and numerical examples are presented in part (Ⅱ).
