In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid ...In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid subjected to distributed follower forces is investigated.Based on the Pflu¨ger column model,the equation of motion for supported pipes subjected concurrently to internal fluid flow and distributed follower forces is established.The analytical model,after Galerkin discretization to two degrees of freedom,is evaluated by analyzing the corresponding eigenvalue problem.The complex frequencies versus fluid velocity are obtained for various system parameters.The results show that either buckling or flutter instabilities could occur in supported fluid-conveying pipes under the action of distributed follower forces,depending on the parameter values of distributed follower forces.展开更多
A method is presented for solving the three-dimensional axisymmet- ric field equations for a perfectly plastic material which obeys the von-Mises yield criterion and the Levy-Mises flow law. The method is used for the...A method is presented for solving the three-dimensional axisymmet- ric field equations for a perfectly plastic material which obeys the von-Mises yield criterion and the Levy-Mises flow law. The method is used for the particular case in which a small axisymmetric perturbed flow is superposed on a uniform flow without flow reversal taking place. The method then leads to solving a fourth order differen- tial equation for the velocity potential. The special case of a thick cylindrical shell under compressive flow is examined. The solution so obtained, being derived from the three dimensional theory, includes a correct treatment of transverse shear distor- tion. A preferred mode of instability is identified having a wave-length in reasonable agreement with that obtained experimentally by other workers.展开更多
This paper presents a closed form solution to the dynamic stability problem of a beam-column system with hinged ends loaded by an axial periodically time-varying compressive force of an elliptic type,i.e.,a1cn 2（τ,...This paper presents a closed form solution to the dynamic stability problem of a beam-column system with hinged ends loaded by an axial periodically time-varying compressive force of an elliptic type,i.e.,a1cn 2（τ,k 2）＋a2sn 2（τ,k 2）＋a3dn 2（τ,k 2）.The solution to the governing equation is obtained in the form of Fourier sine series.The resulting ordinary differential equation is solved analytically.Finding the exact analytical solutions to the dynamic buckling problems is difficult.However,the availability of exact solutions can provide adequate understanding for the physical characteristics of the system.In this study,the frequency-response characteristics of the system,the effects of the static load,the driving forces,and the frequency ratio on the critical buckling load are also investigated.展开更多
The structural instability of multi-walled carbon nanotubes(MWCNTs) has captured extensive attention due to the unique characteristic of extremely thin hollow cylinder structure. The previous studies usually focus on ...The structural instability of multi-walled carbon nanotubes(MWCNTs) has captured extensive attention due to the unique characteristic of extremely thin hollow cylinder structure. The previous studies usually focus on the buckling behavior without considering the effects of the wall number and initial pressure. In this paper, the axial buckling behavior of MWCNTs with the length-to-outermost radius ratio less than 20 is investigated within the framework of the Donnell shell theory. The governing equations for the infinitesimal buckling of MWCNTs are established, accounting for the van der Waals(vd W) interaction between layers. The effects of the wall number, initial pressure prior to buckling, and aspect ratio on the critical buckling mode, buckling load, and buckling strain are discussed, respectively. Specially, the four-walled and twenty-walled CNTs are studied in detail, indicating the fact that the buckling instability may occur in other layers besides the outermost layer. The obtained results extend the buckling analysis of the continuum-based model, and provide theoretical support for the application of CNTs.展开更多
Since the half of the XX century,attention was given to the instability of structures under parametric excitation,especially under periodic loads.On the other hand,the instability of bars subjected to axial loads of i...Since the half of the XX century,attention was given to the instability of structures under parametric excitation,especially under periodic loads.On the other hand,the instability of bars subjected to axial loads of impulsive type has been little studied,in spite of the practical importance of the topic.Thus,in Engineering Design it is frequently supposed,without tests or additional verifications,that an axial load of short duration can exceed the Euler critical load of the bar without inducing damage in the same.Within this context,this paper proposes the use of the truss-like Discrete Element Method(DEM)for determining the dynamic response of elastic straight bars subjected to axial loads defined by pulses of short duration.The proposed approach allows the consideration of initial imperfections,as well as large displacements and other non-linear effects.The influence of the pulse duration and other effects in the response of the bar are also evaluated.Initially,the performance of the proposed methodology is verified in static and dynamic instability problems of homogeneous bars without geometrical imperfections,by comparing the DEM results with analytical solutions available in the literature.After that,the DEM is employed to analyze more complex cases,including bars with initial imperfections and non-homogeneous bars,in which material properties,as Young’s modulus and mass density,are assumed to be correlated Gaussian random fields.The proposed methodology has proven to be a useful and easy tool for analysis of dynamic instability of bars and could therefore be used by designers for estimating the dynamic buckling load.展开更多
The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a ...The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 10802031 and 11172107)the Program for New Century Excellent Talents in Universitythe Fundamental Research Funds for the CentralUniversities,HUST (grant number 2010MS021)
文摘In the past decades,it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported.In this paper,the form of instability of supported pipes conveying fluid subjected to distributed follower forces is investigated.Based on the Pflu¨ger column model,the equation of motion for supported pipes subjected concurrently to internal fluid flow and distributed follower forces is established.The analytical model,after Galerkin discretization to two degrees of freedom,is evaluated by analyzing the corresponding eigenvalue problem.The complex frequencies versus fluid velocity are obtained for various system parameters.The results show that either buckling or flutter instabilities could occur in supported fluid-conveying pipes under the action of distributed follower forces,depending on the parameter values of distributed follower forces.
文摘A method is presented for solving the three-dimensional axisymmet- ric field equations for a perfectly plastic material which obeys the von-Mises yield criterion and the Levy-Mises flow law. The method is used for the particular case in which a small axisymmetric perturbed flow is superposed on a uniform flow without flow reversal taking place. The method then leads to solving a fourth order differen- tial equation for the velocity potential. The special case of a thick cylindrical shell under compressive flow is examined. The solution so obtained, being derived from the three dimensional theory, includes a correct treatment of transverse shear distor- tion. A preferred mode of instability is identified having a wave-length in reasonable agreement with that obtained experimentally by other workers.
文摘This paper presents a closed form solution to the dynamic stability problem of a beam-column system with hinged ends loaded by an axial periodically time-varying compressive force of an elliptic type,i.e.,a1cn 2（τ,k 2）＋a2sn 2（τ,k 2）＋a3dn 2（τ,k 2）.The solution to the governing equation is obtained in the form of Fourier sine series.The resulting ordinary differential equation is solved analytically.Finding the exact analytical solutions to the dynamic buckling problems is difficult.However,the availability of exact solutions can provide adequate understanding for the physical characteristics of the system.In this study,the frequency-response characteristics of the system,the effects of the static load,the driving forces,and the frequency ratio on the critical buckling load are also investigated.
基金Project supported by the National Natural Science Foundation of China (No. 12072003)the Beijing Natural Science Foundation of China (No. 1222001)。
文摘The structural instability of multi-walled carbon nanotubes(MWCNTs) has captured extensive attention due to the unique characteristic of extremely thin hollow cylinder structure. The previous studies usually focus on the buckling behavior without considering the effects of the wall number and initial pressure. In this paper, the axial buckling behavior of MWCNTs with the length-to-outermost radius ratio less than 20 is investigated within the framework of the Donnell shell theory. The governing equations for the infinitesimal buckling of MWCNTs are established, accounting for the van der Waals(vd W) interaction between layers. The effects of the wall number, initial pressure prior to buckling, and aspect ratio on the critical buckling mode, buckling load, and buckling strain are discussed, respectively. Specially, the four-walled and twenty-walled CNTs are studied in detail, indicating the fact that the buckling instability may occur in other layers besides the outermost layer. The obtained results extend the buckling analysis of the continuum-based model, and provide theoretical support for the application of CNTs.
文摘Since the half of the XX century,attention was given to the instability of structures under parametric excitation,especially under periodic loads.On the other hand,the instability of bars subjected to axial loads of impulsive type has been little studied,in spite of the practical importance of the topic.Thus,in Engineering Design it is frequently supposed,without tests or additional verifications,that an axial load of short duration can exceed the Euler critical load of the bar without inducing damage in the same.Within this context,this paper proposes the use of the truss-like Discrete Element Method(DEM)for determining the dynamic response of elastic straight bars subjected to axial loads defined by pulses of short duration.The proposed approach allows the consideration of initial imperfections,as well as large displacements and other non-linear effects.The influence of the pulse duration and other effects in the response of the bar are also evaluated.Initially,the performance of the proposed methodology is verified in static and dynamic instability problems of homogeneous bars without geometrical imperfections,by comparing the DEM results with analytical solutions available in the literature.After that,the DEM is employed to analyze more complex cases,including bars with initial imperfections and non-homogeneous bars,in which material properties,as Young’s modulus and mass density,are assumed to be correlated Gaussian random fields.The proposed methodology has proven to be a useful and easy tool for analysis of dynamic instability of bars and could therefore be used by designers for estimating the dynamic buckling load.
基金Project supported by the National Key Basic Pre-Research Fund of the Ministry of Science and Technology of Chinathe Fund for Outstanding Young Researchers of the National Natural Sciences Foundation of China (No.10025208)+2 种基金 the KeyFund of the National Natural Science Foundation of China the Youth Fund of the National Natural Science Foundationof China (No.10302009) and the Youth Fund of Lanzhou University (Lzu200305).
文摘The magneto-plastic instability of a ferromagnetic beam-type plate with simple supports and small initial imperfection is analytically investigated in this paper for that the plastic deformation of the plate with a linear-strain hardening relation is considered when the plate is located in a strong uniformly distributed magnetic ?eld. After the distribution of magnetic ?elds related to the de?ected con?guration of plate is imaginably divided into two parts, i.e., one is related to the ?at plate and the other dependent on the perturbation of magnetic ?elds for which the plate con?guration changes from the ?at into the deformed state, the perturbation technique is employed to analyze the distribution of the perturbation magnetic ?elds in and out-of the magnetic medium of the ferromagnetic structure in a transverse magnetic ?eld, which leads to some analytical formulae/solutions for the magnetic ?elds and the resulting magnetic force exerted on the plate. Based on them, the magneto-plastic buckling and snapping of the plate in a transverse magnetic ?eld is discussed, and the critical magnetic ?eld is analytically formulated in terms of the parameters of geometry and material of the plate employed by solving the governing equation of the magneto-plastic plate in the applied magnetic ?eld. Further, the sensitivity of the initial imperfection on the magneto-plastic instability, expressed by an ampli?cation function, is obtained by solving the dynamic equation of de?ection of the plate after the inertial force in the transverse direction is taken into account. The results obtained show that the critical magnetic ?eld is sensitive to the plastic characteristic, e.g., hardening coe?cient, and the instability mode and de?ection of the plate are dependent on the geometrical imperfection as well.
