Large deflection postbuckling responses of metamaterial cylindrical shells perforated by arrayed circular holes are investigated through a newly proposed theoretical model incorporating with finite element method and ...Large deflection postbuckling responses of metamaterial cylindrical shells perforated by arrayed circular holes are investigated through a newly proposed theoretical model incorporating with finite element method and experiment.The triggering of an unusual pattern transformation under compressive load(that shows special hyperelastic metamaterial characteristics)contributes to the particularity of the postbucklingmodes,in which the axisymmetric waisted and non-axisymmetric postbuckling configurations of perforated cylindrical shells are identified.The transformations of postbucking modes are mainly affected by global outline sizes of the shell and local geometrical parameters of holes.The structural load-carrying capacity for the waisted postbuckling response suffers a sudden drop and recovers when the holes collapse.Comparatively,the shell would undergo a sustained fall off under non-axisymmetric postbuckling states.The negative Poisson’s ratio induced by pattern transformation plays a key role and a critical effective threshold value exists,inducing the waisted postbuckling mode.The revealed principles would be of benefit for achieving a controllable structural stability that is usually difficult to implement on those conventional structures.展开更多
A nonlocal continuum orthotropic plate model is proposed to study the vibration behavior of single-layer graphene sheets (SLGSs) using an analytical symplectic approach. A Hamiltonian system is established by introduc...A nonlocal continuum orthotropic plate model is proposed to study the vibration behavior of single-layer graphene sheets (SLGSs) using an analytical symplectic approach. A Hamiltonian system is established by introducing a total unknown vector consisting of the displacement amplitude, rotation angle, shear force, and bending moment. The high-order governing differential equation of the vibration of SLGSs is transformed into a set of ordinary differential equations in symplectic space. Exact solutions for free vibration are obtianed by the method of separation of variables without any trial shape functions and can be expanded in series of symplectic eigenfunctions. Analytical frequency equations are derived for all six possible boundary conditions. Vibration modes are expressed in terms of the symplectic eigenfunctions. In the numerical examples, comparison is presented to verify the accuracy of the proposed method. Comprehensive numerical examples for graphene sheets with Levy-type boundary conditions are given. A parametric study of the natural frequency is also included.展开更多
The nonlinear in-plane instability of functionally graded carbon nanotube reinforced composite(FG-CNTRC)shallow circular arches with rotational constraints subject to a uniform radial load in a thermal environment is ...The nonlinear in-plane instability of functionally graded carbon nanotube reinforced composite(FG-CNTRC)shallow circular arches with rotational constraints subject to a uniform radial load in a thermal environment is investigated.Assuming arches with thickness-graded material properties,four different distribution patterns of carbon nanotubes(CNTs)are considered.The classical arch theory and Donnell’s shallow shell theory assumptions are used to evaluate the arch displacement field,and the analytical solutions of buckling equilibrium equations and buckling loads are obtained by using the principle of virtual work.The critical geometric parameters are introduced to determine the criteria for buckling mode switching.Parametric studies are carried out to demonstrate the effects of temperature variations,material parameters,geometric parameters,and elastic constraints on the stability of the arch.It is found that increasing the volume fraction of CNTs and distributing CNTs away from the neutral axis significantly enhance the bending stiffness of the arch.In addition,the pretension and initial displacement caused by the temperature field have significant effects on the buckling behavior.展开更多
Bearing as an important machine element is widely used for industrial and automotive applications.At certain operational speed,bearings induce disturbing vibrations and noises that affect machine service life,producti...Bearing as an important machine element is widely used for industrial and automotive applications.At certain operational speed,bearings induce disturbing vibrations and noises that affect machine service life,productivity and passenger comfort in case of vehicle applications.Dissipative elastic metamaterials have caught considerable attention of scientific community due to their effective medium properties and peculiar dynamic characteristics including frequency bandgaps that can be effectively applied to attenuate and control undesirable vibration and noises.Although a substantial amount of theoretical work for effective medium characteristics and dynamic properties of acoustic/elastic metamaterials has been reported,the practical design and application of these composite structures for real-life engineering problems still remain unexplored.The present study intends to investigate a potential application of dissipative elastic metamaterials in controlling the bearing-generated vibration and noises over an ultrawide frequency range.The study is based on a simple analytical model together with rigorous finite element numerical simulations.It has been established that the dissipative characteristic of resonant system caused by larger material mismatch broadens the local resonance bandgaps beyond the bounding resonance frequency at the cost of wave transmission.In order to achieve broadband vibration and noise control,multi-resonant composite structures are embedded inside the bearing housing in five different layers.The reported results revealed the presence of broadband wave attenuation zone distributed from 3 to 52 kHz with consideration of material damping.The bearing-generated vibration and noises lying inside the wave attenuation zone will be mitigated.This feasibility study provides a new concept for the design and application of acoustic/elastic metamaterials in the bearing industry to improve machine service life and to enhance productivity and passenger comfort.展开更多
In this article,we introduce a complete set of constitutive relations and field equations for the linear reduced micromorphic model.We further investigate the internal variables and their relationship in the case of t...In this article,we introduce a complete set of constitutive relations and field equations for the linear reduced micromorphic model.We further investigate the internal variables and their relationship in the case of two-dimensional(2D)wave propagation.The dynamic response is investigated for composite materials,which is due to an external wave in two dimensions applied at the boundary of the considered domain.Analytical solutions for the model are unavailable at this stage due to dependency of the field equations on spatial and time variables in a complicated manner.A finite element approach is adopted to derive approximate solutions for the field equations,and numerical finite element solutions for the internal fields are presented in detail and discussed.展开更多
Secure information retrieval is an essential task in today's highly digitised society.In some applications,it may be necessary that user query's privacy and database content's security are enforced.For the...Secure information retrieval is an essential task in today's highly digitised society.In some applications,it may be necessary that user query's privacy and database content's security are enforced.For these settings,symmetric private information retrieval(SPIR)could be employed,but its implementation is known to be demanding,requiring a private key-exchange network as the base layer.Here,we report for the first time a realisation of provably-secure SPIR supported by a quantum-secure key-exchange network.The SPIR scheme looks at biometric security,offering secure retrieval of 582-byte fingerprint files from a database with 800 entries.Our experimental results clearly demonstrate the feasibility of SPIR with quantum secure communications,thereby opening up new possibilities in secure distributed data storage and cloud computinq over the future Quantum Internet.展开更多
基金State Key Laboratory of Structural Analysis for Industrial Equipment(S22303)Fundamental Research Funds for the CentralUniversities(DUT22LK16,DUT21LK35)National Natural Science Foundation of China(12002071).
文摘Large deflection postbuckling responses of metamaterial cylindrical shells perforated by arrayed circular holes are investigated through a newly proposed theoretical model incorporating with finite element method and experiment.The triggering of an unusual pattern transformation under compressive load(that shows special hyperelastic metamaterial characteristics)contributes to the particularity of the postbucklingmodes,in which the axisymmetric waisted and non-axisymmetric postbuckling configurations of perforated cylindrical shells are identified.The transformations of postbucking modes are mainly affected by global outline sizes of the shell and local geometrical parameters of holes.The structural load-carrying capacity for the waisted postbuckling response suffers a sudden drop and recovers when the holes collapse.Comparatively,the shell would undergo a sustained fall off under non-axisymmetric postbuckling states.The negative Poisson’s ratio induced by pattern transformation plays a key role and a critical effective threshold value exists,inducing the waisted postbuckling mode.The revealed principles would be of benefit for achieving a controllable structural stability that is usually difficult to implement on those conventional structures.
基金support of the National Natural Science Foundation of China (Grant 11672054)the Research Grant Council of Hong Kong (11215415)the National Basic Research Program of China (973 Program) (Grant 2014CB046803)
文摘A nonlocal continuum orthotropic plate model is proposed to study the vibration behavior of single-layer graphene sheets (SLGSs) using an analytical symplectic approach. A Hamiltonian system is established by introducing a total unknown vector consisting of the displacement amplitude, rotation angle, shear force, and bending moment. The high-order governing differential equation of the vibration of SLGSs is transformed into a set of ordinary differential equations in symplectic space. Exact solutions for free vibration are obtianed by the method of separation of variables without any trial shape functions and can be expanded in series of symplectic eigenfunctions. Analytical frequency equations are derived for all six possible boundary conditions. Vibration modes are expressed in terms of the symplectic eigenfunctions. In the numerical examples, comparison is presented to verify the accuracy of the proposed method. Comprehensive numerical examples for graphene sheets with Levy-type boundary conditions are given. A parametric study of the natural frequency is also included.
基金Project supported by the National Natural Science Foundation of China (Nos.11972240 and 51875374)。
文摘The nonlinear in-plane instability of functionally graded carbon nanotube reinforced composite(FG-CNTRC)shallow circular arches with rotational constraints subject to a uniform radial load in a thermal environment is investigated.Assuming arches with thickness-graded material properties,four different distribution patterns of carbon nanotubes(CNTs)are considered.The classical arch theory and Donnell’s shallow shell theory assumptions are used to evaluate the arch displacement field,and the analytical solutions of buckling equilibrium equations and buckling loads are obtained by using the principle of virtual work.The critical geometric parameters are introduced to determine the criteria for buckling mode switching.Parametric studies are carried out to demonstrate the effects of temperature variations,material parameters,geometric parameters,and elastic constraints on the stability of the arch.It is found that increasing the volume fraction of CNTs and distributing CNTs away from the neutral axis significantly enhance the bending stiffness of the arch.In addition,the pretension and initial displacement caused by the temperature field have significant effects on the buckling behavior.
基金The work described in this paper was supported by General Research Grants from the Research Grants Council of the Hong Kong Special Administrative Region(Project No.CityU 11216318)City University of Hong Kong(Project No.9680213)。
文摘Bearing as an important machine element is widely used for industrial and automotive applications.At certain operational speed,bearings induce disturbing vibrations and noises that affect machine service life,productivity and passenger comfort in case of vehicle applications.Dissipative elastic metamaterials have caught considerable attention of scientific community due to their effective medium properties and peculiar dynamic characteristics including frequency bandgaps that can be effectively applied to attenuate and control undesirable vibration and noises.Although a substantial amount of theoretical work for effective medium characteristics and dynamic properties of acoustic/elastic metamaterials has been reported,the practical design and application of these composite structures for real-life engineering problems still remain unexplored.The present study intends to investigate a potential application of dissipative elastic metamaterials in controlling the bearing-generated vibration and noises over an ultrawide frequency range.The study is based on a simple analytical model together with rigorous finite element numerical simulations.It has been established that the dissipative characteristic of resonant system caused by larger material mismatch broadens the local resonance bandgaps beyond the bounding resonance frequency at the cost of wave transmission.In order to achieve broadband vibration and noise control,multi-resonant composite structures are embedded inside the bearing housing in five different layers.The reported results revealed the presence of broadband wave attenuation zone distributed from 3 to 52 kHz with consideration of material damping.The bearing-generated vibration and noises lying inside the wave attenuation zone will be mitigated.This feasibility study provides a new concept for the design and application of acoustic/elastic metamaterials in the bearing industry to improve machine service life and to enhance productivity and passenger comfort.
文摘In this article,we introduce a complete set of constitutive relations and field equations for the linear reduced micromorphic model.We further investigate the internal variables and their relationship in the case of two-dimensional(2D)wave propagation.The dynamic response is investigated for composite materials,which is due to an external wave in two dimensions applied at the boundary of the considered domain.Analytical solutions for the model are unavailable at this stage due to dependency of the field equations on spatial and time variables in a complicated manner.A finite element approach is adopted to derive approximate solutions for the field equations,and numerical finite element solutions for the internal fields are presented in detail and discussed.
基金This research is supported by the National Research Foundation(NRF)Singapore,under its NRF Fellowship programme(NRFF11-2019-0001)Quantum Engineering Programme 1.0 projects(QEP-P2,QEP-P3,and QEP-P8).
文摘Secure information retrieval is an essential task in today's highly digitised society.In some applications,it may be necessary that user query's privacy and database content's security are enforced.For these settings,symmetric private information retrieval(SPIR)could be employed,but its implementation is known to be demanding,requiring a private key-exchange network as the base layer.Here,we report for the first time a realisation of provably-secure SPIR supported by a quantum-secure key-exchange network.The SPIR scheme looks at biometric security,offering secure retrieval of 582-byte fingerprint files from a database with 800 entries.Our experimental results clearly demonstrate the feasibility of SPIR with quantum secure communications,thereby opening up new possibilities in secure distributed data storage and cloud computinq over the future Quantum Internet.
