A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigate...A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigated by the generalized differential quadrature rule (GDQR) method. The GDQR method is also used to calculate the forced vibration response of the beam and voltage of each piezoelectric layer when the beam is subject to a sinusoidal base excitation. Results obtained from the analytical method are compared with those obtained from the finite element simulation with ANSYS, and good agreement is found. The voltage output of this periodic beam over its first band gap is calculated and compared with the voltage output of the uniform piezoelectric beam. It is concluded that this periodic beam has three advantages over the uniform piezoelectric beam, i.e., generating more voltage outputs over a wide frequency range, absorbing vibration, and being less weight.展开更多
The bending and free vibrational behaviors of functionally graded(FG)cylindrical beams with radially and axially varying material inhomogeneities are investigated.Based on a high-order cylindrical beam model,where the...The bending and free vibrational behaviors of functionally graded(FG)cylindrical beams with radially and axially varying material inhomogeneities are investigated.Based on a high-order cylindrical beam model,where the shear deformation and rotary inertia are both considered,the two coupled governing differential motion equations for the deflection and rotation are established.The analytical bending solutions for various boundary conditions are derived.In the vibrational analysis of FG cylindrical beams,the two governing equations are firstly changed to a single equation by means of an auxiliary function,and then the vibration mode is expanded into shifted Chebyshev polynomials.Numerical examples are given to investigate the effects of the material gradient indices on the deflections,the stress distributions,and the eigenfrequencies of the cylindrical beams,respectively.By comparing the obtained numerical results with those obtained by the three-dimensional(3D)elasticity theory and the Timoshenko beam theory,the effectiveness of the present approach is verified.展开更多
The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients....The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients. By decomposing the variable flexural stiffness and mass per unit length into reference invariant and variant parts, the perturbation theory is introduced to obtain an approximate analytical formula of the natural frequencies of the non-uniform AFG beams with different boundary conditions.Furthermore, assuming polynomial distributions of Young's modulus and the mass density, the numerical results of the AFG beams with various taper ratios are obtained and compared with the published literature results. The discussion results illustrate that the proposed method yields an effective estimate of the first three order natural frequencies for the AFG tapered beams. However, the errors increase with the increase in the mode orders especially for the cases with variable heights. In brief, the asymptotic development method is verified to be simple and efficient to analytically study the free vibration of non-uniform AFG beams, and it could be used to analyze any tapered beams with an arbitrary varying cross width.展开更多
A multi-objective optimization of non-uniform beams is presented for minimum radiated sound power and weight. The transfer matrix method is used to compute the structural and acoustic responses of a non-uniform beam a...A multi-objective optimization of non-uniform beams is presented for minimum radiated sound power and weight. The transfer matrix method is used to compute the structural and acoustic responses of a non-uniform beam accurately and efficiently. The multi-objective particle swarm optimization technique is applied to search the Pareto optimal solutions that represent various compromises between weight and sound radiation. Several constraints are imposed, which substantially reduce the volume fraction of feasible solutions in the design space. Two nonuniform beams with different boundary conditions are studied to demonstrate the multi-objective optimal designs of the structure.展开更多
The two coupled governing differential equations for the out-of-plane vibrations of non-uniform beams with variable curvature are derived via the Hamilton’s principle.These equations are expressed in terms of flexura...The two coupled governing differential equations for the out-of-plane vibrations of non-uniform beams with variable curvature are derived via the Hamilton’s principle.These equations are expressed in terms of flexural and torsional displacements simultaneously.In this study,the analytical method is proposed.Firstly,two physical parameters are introduced to simplify the analysis.One derives the explicit relations between the flexural and the torsional displacements which can also be used to reduce the difficulty in experimental measurements.Based on the relation,the two governing characteristic differential equations with variable coefficients can be uncoupled into a sixth-order ordinary differential equation in terms of the flexural displacement only.When the material and geometric properties of the beam are in arbitrary polynomial forms,the exact solutions with regard to the outof-plane vibrations of non-uniform beams with variable curvature can be obtained by the recurrence formula.In addition,the mode transition mechanism is revealed and the influence of several parameters on the vibration of the non-uniform beam with variable curvature is explored.展开更多
In order to simulate the coupling vibration of a vehicle or train moves on a multi-span continuous bridge with non-uniform cross sections, a moving mass model is used according to the Finite Element Method, the effect...In order to simulate the coupling vibration of a vehicle or train moves on a multi-span continuous bridge with non-uniform cross sections, a moving mass model is used according to the Finite Element Method, the effect of the inertial force, Coriolis force and centrifugal force are considered by means of the additive matrices. For a non-uniform rectangular section beam with both linear and parabolic variable heights in a plane, the stiffness and mass matrices of the beam elements are presented. For a non-uniform box girder, Romberg numerical integral scheme is adopted, each coefficient of the stiffness matrix is obtained by means of a normal numerical computation. By applying these elements to calculate the non-uniform beam, the computational accuracy and efficiency are improved. The finite element method program is worked out and an entire dynamic response process of the beam with non-uniform cross sections subjected to a moving mass is simulated numerically, the results are compared to those previously published for some simple examples. For some complex multi-span bridges subjected to some moving vehicles with changeable velocity and friction, the computational results, which can be regarded as a reference for engineering design and scientific research, are also given simultaneously.展开更多
Free and steady state forced transverse vibrations of non-uniform beams are investigated with a proposed method, leading to a series solution. The obtained series is verified to be convergent and linearly independent ...Free and steady state forced transverse vibrations of non-uniform beams are investigated with a proposed method, leading to a series solution. The obtained series is verified to be convergent and linearly independent in a convergence test and by the non-zero value of the corresponding Wronski determinant, respectively. The obtained solution is rigorous, which can be reduced to a classical solution for uniform beams. The proposed method can deal with arbitrary non-uniform Euler-Bernoulli beams in principle, but the methods in terms of special functions or elementary functions can only work in some special cases.展开更多
Heavy-ion-driven fusion (HIF) is a scheme to achieve inertial confinement fusion (ICF). Investigation of the non-uniformity of heavy-ion beam (HIB) irradiation is one of the key issues for ICF driven by powerful...Heavy-ion-driven fusion (HIF) is a scheme to achieve inertial confinement fusion (ICF). Investigation of the non-uniformity of heavy-ion beam (HIB) irradiation is one of the key issues for ICF driven by powerful heavy-ion beams. Ions in HIB impinge on the pellet surface and deposit their energy in a relatively deep and wide area. Therefore, the non-uniformity of HIB irradiation should be evaluated in the volume of the deposition area in the absorber layer. By using the OK1 code with some corrections, the non-uniformity of heavy-ion beam irradiation for the different ion beams on two kinds of targets were evaluated in 12-beam, 20-beam, 60-beam and 120-beam irradiation schemes. The root-mean-square (RMS) non-uniformity value becomes aRMS = 8.39% in an aluminum mono-layer pellet structure and aRMS = 6.53% in a lead-aluminum layer target for the 12-uranium-beam system. The RMS non-uniformity for the lead-aluminum layer target was lower than that for the mono-layer target. The RMS and peak-to-valley (PTV) non-uniformities are reduced with the increase in beam number, and low at the Bragg peak layer.展开更多
The non-uniform beam components are commonly used in engineering,while the method to analyze such component is not too satisfactory yet. A new non-uniform beam element with high precision was developed based on the no...The non-uniform beam components are commonly used in engineering,while the method to analyze such component is not too satisfactory yet. A new non-uniform beam element with high precision was developed based on the non-linear analysis and the static condensation. Based on the interpolation theory, the displacement fields of the three-node non-uniform Euler-Bernoulli beam element were constructed at first: the quintic Hermite interpolation polynomial was used for the lateral displacement field and the quadratic Lagrange interpolation polynomial for the axial displacement field. Then,based on the basic assumptions of non-uniform Euler-Bernoulli beam whose section properties were continuously varying along its centroidal axis, the linear and geometric stiffness matrices of the three-node non-uniform beam element were derived according to the nonlinear finite element theory. Finally,the degrees of freedom ( DOFs) of the middle node of the element were eliminated using the static condensation method, and a new two-node non-uniform beam element including axial-force effect was obtained. The results indicate that each bar needs to be meshed with only one element could get a fairly accurate solution when it is applied to the stability analyses.展开更多
In this paper, the step reduction method is discussed, which was advanced by Prof. Yeh Kai-yuan for calculating a non-uniform beam with various sections. The following result is proved. The approximate solution by thi...In this paper, the step reduction method is discussed, which was advanced by Prof. Yeh Kai-yuan for calculating a non-uniform beam with various sections. The following result is proved. The approximate solution by this method approaches the true solution if the number of the steps approaches the infinity. However, the measure of the error between the limit solution and the ture solution is not in the pure mathematics sense but in the mechanics sense.展开更多
For the static analysis of the sinking stage curved beam, a finite difference model was presented based on the proposed revised Vlasov equations. First, revised Vlasov equations for thin-walled curved beams with close...For the static analysis of the sinking stage curved beam, a finite difference model was presented based on the proposed revised Vlasov equations. First, revised Vlasov equations for thin-walled curved beams with closed sections were deduced considering the shear strain on the mid-surface of the cross-section. Then, the finite difference formulation of revised Vlasov equations was implemented with the parabolic interpolation based on Taylor series. At last, the finite difference model was built by substituting geometry and boundary conditions of the sinking stage curved beam into the finite difference formulation. The validity of present work is confirmed by the published literature and ANSYS simulation results. It can be concluded that revised Vlasov equations are more accurate than the original one in the analysis of thin-walled beams with closed sections, and that present finite difference model is applicable in the evaluation of the sinking stage curved beam.展开更多
The problem of quick analysis using exact geometry data was proposed by Hughes et al. and the isogeometric analysis framework was introduced as a solution. In this letter, the exact geometry concept is combined into t...The problem of quick analysis using exact geometry data was proposed by Hughes et al. and the isogeometric analysis framework was introduced as a solution. In this letter, the exact geometry concept is combined into the quasi-conforming framework and a novel method, i.e., the exact geometry based quasi-conforming analysis is proposed. In present method the geometry is exactly described by non-uniform rational B-spline bases, while the solution space by traditional polynomial bases. Present method combines the merits of both isogeometric analysis and quasi-conforming finite element method. In this letter Euler-Bernoulli beam problem is solved as an example and the results show that the present method is effective and promising.展开更多
Stiffened plates or shells are widely used in engineering structures as primary or secondary load-bearing components.How to design the layout and sizes of the stiffeners is of great significance for structural lightwe...Stiffened plates or shells are widely used in engineering structures as primary or secondary load-bearing components.How to design the layout and sizes of the stiffeners is of great significance for structural lightweight.In this work,a new topology optimization method for simultaneously optimizing the layout and cross-section topology of the stiffeners is developed to solve this issue.The stilfeners and base plates are modeled by the beam and shell elements,respectively,significantly reducing the computational cost.The Giavotto beam theory,instead of the widely employed Euler or Timoshenko beam theory,is applied to model the stiffeners for considering the warping deformation in evaluating the section stiffness of the beam.A multi-scale topology optimization model is established by simultaneously optimizing the layout of the beam and the topology of the cross-section.The design space is significantly expanded by optimizing these two types of design variables.Several numerical examples are applied to illustrate the validity and effectiveness of the proposed method.The results show that the proposed two-scale optimization approach can generate better designs than the single-scale method.展开更多
For the accuracy of experimental results, preparing a high quality polished surface and cross-section of the materials for further analysis using electron backscattered diffraction (EBSD), electron probe microanalysis...For the accuracy of experimental results, preparing a high quality polished surface and cross-section of the materials for further analysis using electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA), and scanning probe microscopy (SPM) is extremely important. Broad ion beam (BIB) polishing, a method based on the principle of ion bombardment, has irreplaceable advantages. It makes up for the drawbacks and limitations of traditional polishing methods such as mechanical polishing, electrochemical polishing, and chemical polishing. The ions will not leave the bombardment area during polishing, which makes the BIB method suitable for porous materials. The energy of the ion beam can be adjusted according to the sample to reduce the deformation and strain of the polishing area, especially for fragile, soft, and hard materials. The conditions that need to be controlled during BIB polishing are simple. This paper demonstrated the unique advantages of BIB polishing technology in porous, layered and powder materials characterization through some typical application examples, and guided more researchers to understand and utilize BIB polishing technology in the development of new applications.展开更多
Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band,in this paper,we use the Pancharatnam-Berry(PB)phase concept to propose a high-efficienc...Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band,in this paper,we use the Pancharatnam-Berry(PB)phase concept to propose a high-efficiency reflectivetype coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities.By optimizing the coding sequences,we demonstrate that the designed 1-,2-,and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves.The two proposed1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled.For normally incident x-and y-polarized waves,a 10 d B radar cross-section(RCS)reduction can be achieved from 2.1 THz to5.2 THz using the designed 2-bit coding metasurface.Moreover,two kinds of orbital angular momentum(OAM)vortex beams with different moduli are generated by a coding metasurface using different coding sequences.Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves,and contributes to the development of metasurfaces towards practical applications.展开更多
Vibration energy harvesters(VEHs) can transform ambient vibration energy to electricity and have been widely investigated as promising self-powered devices for wireless sensor networks, wearable sensors, and applicati...Vibration energy harvesters(VEHs) can transform ambient vibration energy to electricity and have been widely investigated as promising self-powered devices for wireless sensor networks, wearable sensors, and applications of a micro-electro-mechanical system(MEMS). However, the ambient vibration is always too weak to hinder the high energy conversion efficiency. In this paper, the integrated frame composed of piezoelectric beams and mechanical amplifiers is proposed to improve the energy conversion efficiency of a VEH. First, the initial structures of a piezoelectric frame(PF) and an amplification frame(AF) are designed. The dynamic model is then established to analyze the influence of key structural parameters on the mechanical amplification factor. Finite element simulation is conducted to study the energy harvesting performance, where the stiffness characteristics and power output in the cases of series and parallel load resistance are discussed in detail. Furthermore, piezoelectric beams with variable cross-sections are introduced to optimize and improve the energy harvesting efficiency. Advantages of the PF with the AF are illustrated by comparison with conventional piezoelectric cantilever beams. The results show that the proposed integrated VEH has a good mechanical amplification capability and is more suitable for low-frequency vibration conditions.展开更多
文摘A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigated by the generalized differential quadrature rule (GDQR) method. The GDQR method is also used to calculate the forced vibration response of the beam and voltage of each piezoelectric layer when the beam is subject to a sinusoidal base excitation. Results obtained from the analytical method are compared with those obtained from the finite element simulation with ANSYS, and good agreement is found. The voltage output of this periodic beam over its first band gap is calculated and compared with the voltage output of the uniform piezoelectric beam. It is concluded that this periodic beam has three advantages over the uniform piezoelectric beam, i.e., generating more voltage outputs over a wide frequency range, absorbing vibration, and being less weight.
基金Project supported by the Natural Science Foundation of Guangdong Province of China(No.2018A030313258)。
文摘The bending and free vibrational behaviors of functionally graded(FG)cylindrical beams with radially and axially varying material inhomogeneities are investigated.Based on a high-order cylindrical beam model,where the shear deformation and rotary inertia are both considered,the two coupled governing differential motion equations for the deflection and rotation are established.The analytical bending solutions for various boundary conditions are derived.In the vibrational analysis of FG cylindrical beams,the two governing equations are firstly changed to a single equation by means of an auxiliary function,and then the vibration mode is expanded into shifted Chebyshev polynomials.Numerical examples are given to investigate the effects of the material gradient indices on the deflections,the stress distributions,and the eigenfrequencies of the cylindrical beams,respectively.By comparing the obtained numerical results with those obtained by the three-dimensional(3D)elasticity theory and the Timoshenko beam theory,the effectiveness of the present approach is verified.
基金Project supported by the National Natural Science Foundation of China(No.11672008)
文摘The asymptotic development method is applied to analyze the free vibration of non-uniform axially functionally graded(AFG) beams, of which the governing equations are differential equations with variable coefficients. By decomposing the variable flexural stiffness and mass per unit length into reference invariant and variant parts, the perturbation theory is introduced to obtain an approximate analytical formula of the natural frequencies of the non-uniform AFG beams with different boundary conditions.Furthermore, assuming polynomial distributions of Young's modulus and the mass density, the numerical results of the AFG beams with various taper ratios are obtained and compared with the published literature results. The discussion results illustrate that the proposed method yields an effective estimate of the first three order natural frequencies for the AFG tapered beams. However, the errors increase with the increase in the mode orders especially for the cases with variable heights. In brief, the asymptotic development method is verified to be simple and efficient to analytically study the free vibration of non-uniform AFG beams, and it could be used to analyze any tapered beams with an arbitrary varying cross width.
基金supported by the National Natural Science Foundation of China (No. 51606180)
文摘A multi-objective optimization of non-uniform beams is presented for minimum radiated sound power and weight. The transfer matrix method is used to compute the structural and acoustic responses of a non-uniform beam accurately and efficiently. The multi-objective particle swarm optimization technique is applied to search the Pareto optimal solutions that represent various compromises between weight and sound radiation. Several constraints are imposed, which substantially reduce the volume fraction of feasible solutions in the design space. Two nonuniform beams with different boundary conditions are studied to demonstrate the multi-objective optimal designs of the structure.
文摘The two coupled governing differential equations for the out-of-plane vibrations of non-uniform beams with variable curvature are derived via the Hamilton’s principle.These equations are expressed in terms of flexural and torsional displacements simultaneously.In this study,the analytical method is proposed.Firstly,two physical parameters are introduced to simplify the analysis.One derives the explicit relations between the flexural and the torsional displacements which can also be used to reduce the difficulty in experimental measurements.Based on the relation,the two governing characteristic differential equations with variable coefficients can be uncoupled into a sixth-order ordinary differential equation in terms of the flexural displacement only.When the material and geometric properties of the beam are in arbitrary polynomial forms,the exact solutions with regard to the outof-plane vibrations of non-uniform beams with variable curvature can be obtained by the recurrence formula.In addition,the mode transition mechanism is revealed and the influence of several parameters on the vibration of the non-uniform beam with variable curvature is explored.
文摘In order to simulate the coupling vibration of a vehicle or train moves on a multi-span continuous bridge with non-uniform cross sections, a moving mass model is used according to the Finite Element Method, the effect of the inertial force, Coriolis force and centrifugal force are considered by means of the additive matrices. For a non-uniform rectangular section beam with both linear and parabolic variable heights in a plane, the stiffness and mass matrices of the beam elements are presented. For a non-uniform box girder, Romberg numerical integral scheme is adopted, each coefficient of the stiffness matrix is obtained by means of a normal numerical computation. By applying these elements to calculate the non-uniform beam, the computational accuracy and efficiency are improved. The finite element method program is worked out and an entire dynamic response process of the beam with non-uniform cross sections subjected to a moving mass is simulated numerically, the results are compared to those previously published for some simple examples. For some complex multi-span bridges subjected to some moving vehicles with changeable velocity and friction, the computational results, which can be regarded as a reference for engineering design and scientific research, are also given simultaneously.
基金Project supported by the National Natural Science Foundation of China(Nos.11072157,11272219,11227201,and 10932006)the National Basic Research Program of China(No.2012CB723301)the Training Program for Leading Talent in University Innovative Research Team in Hebei Province(No.LJRC006)
文摘Free and steady state forced transverse vibrations of non-uniform beams are investigated with a proposed method, leading to a series solution. The obtained series is verified to be convergent and linearly independent in a convergence test and by the non-zero value of the corresponding Wronski determinant, respectively. The obtained solution is rigorous, which can be reduced to a classical solution for uniform beams. The proposed method can deal with arbitrary non-uniform Euler-Bernoulli beams in principle, but the methods in terms of special functions or elementary functions can only work in some special cases.
文摘Heavy-ion-driven fusion (HIF) is a scheme to achieve inertial confinement fusion (ICF). Investigation of the non-uniformity of heavy-ion beam (HIB) irradiation is one of the key issues for ICF driven by powerful heavy-ion beams. Ions in HIB impinge on the pellet surface and deposit their energy in a relatively deep and wide area. Therefore, the non-uniformity of HIB irradiation should be evaluated in the volume of the deposition area in the absorber layer. By using the OK1 code with some corrections, the non-uniformity of heavy-ion beam irradiation for the different ion beams on two kinds of targets were evaluated in 12-beam, 20-beam, 60-beam and 120-beam irradiation schemes. The root-mean-square (RMS) non-uniformity value becomes aRMS = 8.39% in an aluminum mono-layer pellet structure and aRMS = 6.53% in a lead-aluminum layer target for the 12-uranium-beam system. The RMS non-uniformity for the lead-aluminum layer target was lower than that for the mono-layer target. The RMS and peak-to-valley (PTV) non-uniformities are reduced with the increase in beam number, and low at the Bragg peak layer.
文摘The non-uniform beam components are commonly used in engineering,while the method to analyze such component is not too satisfactory yet. A new non-uniform beam element with high precision was developed based on the non-linear analysis and the static condensation. Based on the interpolation theory, the displacement fields of the three-node non-uniform Euler-Bernoulli beam element were constructed at first: the quintic Hermite interpolation polynomial was used for the lateral displacement field and the quadratic Lagrange interpolation polynomial for the axial displacement field. Then,based on the basic assumptions of non-uniform Euler-Bernoulli beam whose section properties were continuously varying along its centroidal axis, the linear and geometric stiffness matrices of the three-node non-uniform beam element were derived according to the nonlinear finite element theory. Finally,the degrees of freedom ( DOFs) of the middle node of the element were eliminated using the static condensation method, and a new two-node non-uniform beam element including axial-force effect was obtained. The results indicate that each bar needs to be meshed with only one element could get a fairly accurate solution when it is applied to the stability analyses.
文摘In this paper, the step reduction method is discussed, which was advanced by Prof. Yeh Kai-yuan for calculating a non-uniform beam with various sections. The following result is proved. The approximate solution by this method approaches the true solution if the number of the steps approaches the infinity. However, the measure of the error between the limit solution and the ture solution is not in the pure mathematics sense but in the mechanics sense.
基金Project(IRT1292)supported by Fund for Changjiang Scholars and Innovative Research Team in University(PCSIRT)China+2 种基金Project(51475456)supported by the National Natural Science Foundation of ChinaProject supported by the Priority Academic Program Development(PAPD)of Jiangsu Higher Education InstitutionsChina
文摘For the static analysis of the sinking stage curved beam, a finite difference model was presented based on the proposed revised Vlasov equations. First, revised Vlasov equations for thin-walled curved beams with closed sections were deduced considering the shear strain on the mid-surface of the cross-section. Then, the finite difference formulation of revised Vlasov equations was implemented with the parabolic interpolation based on Taylor series. At last, the finite difference model was built by substituting geometry and boundary conditions of the sinking stage curved beam into the finite difference formulation. The validity of present work is confirmed by the published literature and ANSYS simulation results. It can be concluded that revised Vlasov equations are more accurate than the original one in the analysis of thin-walled beams with closed sections, and that present finite difference model is applicable in the evaluation of the sinking stage curved beam.
基金supported by the Key Project of the National Natural Science Foundation of China(10932003,11272075)the National Basic Research Program of China(2010CB832700)"04"Great Project of Ministry of Industrialization and Information of China(2011ZX04001-21)
文摘The problem of quick analysis using exact geometry data was proposed by Hughes et al. and the isogeometric analysis framework was introduced as a solution. In this letter, the exact geometry concept is combined into the quasi-conforming framework and a novel method, i.e., the exact geometry based quasi-conforming analysis is proposed. In present method the geometry is exactly described by non-uniform rational B-spline bases, while the solution space by traditional polynomial bases. Present method combines the merits of both isogeometric analysis and quasi-conforming finite element method. In this letter Euler-Bernoulli beam problem is solved as an example and the results show that the present method is effective and promising.
基金The authors gratefully acknowledge the financial support to this work from the National Natural Science Foundation of China(Grants 11802164 and U1808215)Shandong Provincial Natural Science Foundation(Grant ZR2019BEE005)the project funded by China Postdoctoral Science Foundation.
文摘Stiffened plates or shells are widely used in engineering structures as primary or secondary load-bearing components.How to design the layout and sizes of the stiffeners is of great significance for structural lightweight.In this work,a new topology optimization method for simultaneously optimizing the layout and cross-section topology of the stiffeners is developed to solve this issue.The stilfeners and base plates are modeled by the beam and shell elements,respectively,significantly reducing the computational cost.The Giavotto beam theory,instead of the widely employed Euler or Timoshenko beam theory,is applied to model the stiffeners for considering the warping deformation in evaluating the section stiffness of the beam.A multi-scale topology optimization model is established by simultaneously optimizing the layout of the beam and the topology of the cross-section.The design space is significantly expanded by optimizing these two types of design variables.Several numerical examples are applied to illustrate the validity and effectiveness of the proposed method.The results show that the proposed two-scale optimization approach can generate better designs than the single-scale method.
基金The authors are grateful for financial supports by the Science and Technology Major Project of Ningbo (Grant No. 2015S1001)the Youth Innovation Promotion Association CAS (Grant No. 2016273)+1 种基金the Ningbo Natural Science Foundation (Grant No. 2017A610039)the Ningbo Science and Technology Plan Projects (Grant No. 2017F10015).
文摘For the accuracy of experimental results, preparing a high quality polished surface and cross-section of the materials for further analysis using electron backscattered diffraction (EBSD), electron probe microanalysis (EPMA), and scanning probe microscopy (SPM) is extremely important. Broad ion beam (BIB) polishing, a method based on the principle of ion bombardment, has irreplaceable advantages. It makes up for the drawbacks and limitations of traditional polishing methods such as mechanical polishing, electrochemical polishing, and chemical polishing. The ions will not leave the bombardment area during polishing, which makes the BIB method suitable for porous materials. The energy of the ion beam can be adjusted according to the sample to reduce the deformation and strain of the polishing area, especially for fragile, soft, and hard materials. The conditions that need to be controlled during BIB polishing are simple. This paper demonstrated the unique advantages of BIB polishing technology in porous, layered and powder materials characterization through some typical application examples, and guided more researchers to understand and utilize BIB polishing technology in the development of new applications.
基金Project supported by the National Natural Science Foundation of China(Grant No.61865008)Northwest Normal University Young Teachers’Scientific Research Capability Upgrading Program(Grant No.NWNU-LKQN2020-11)the Scientific Research Fund of Sichuan Provincial Science and Technology Department,China(Grant No.2020YJ0137)。
文摘Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band,in this paper,we use the Pancharatnam-Berry(PB)phase concept to propose a high-efficiency reflectivetype coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities.By optimizing the coding sequences,we demonstrate that the designed 1-,2-,and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves.The two proposed1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled.For normally incident x-and y-polarized waves,a 10 d B radar cross-section(RCS)reduction can be achieved from 2.1 THz to5.2 THz using the designed 2-bit coding metasurface.Moreover,two kinds of orbital angular momentum(OAM)vortex beams with different moduli are generated by a coding metasurface using different coding sequences.Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves,and contributes to the development of metasurfaces towards practical applications.
基金Project supported by the National Natural Science Foundation of China (Nos. 11972051 and11672008)the Opening Project Foundation of the State Key Laboratory of Mechanical Behavior and System Safety of Traffic Engineering Structures (No. KF-2020-11)。
文摘Vibration energy harvesters(VEHs) can transform ambient vibration energy to electricity and have been widely investigated as promising self-powered devices for wireless sensor networks, wearable sensors, and applications of a micro-electro-mechanical system(MEMS). However, the ambient vibration is always too weak to hinder the high energy conversion efficiency. In this paper, the integrated frame composed of piezoelectric beams and mechanical amplifiers is proposed to improve the energy conversion efficiency of a VEH. First, the initial structures of a piezoelectric frame(PF) and an amplification frame(AF) are designed. The dynamic model is then established to analyze the influence of key structural parameters on the mechanical amplification factor. Finite element simulation is conducted to study the energy harvesting performance, where the stiffness characteristics and power output in the cases of series and parallel load resistance are discussed in detail. Furthermore, piezoelectric beams with variable cross-sections are introduced to optimize and improve the energy harvesting efficiency. Advantages of the PF with the AF are illustrated by comparison with conventional piezoelectric cantilever beams. The results show that the proposed integrated VEH has a good mechanical amplification capability and is more suitable for low-frequency vibration conditions.