The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The r...The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the eff ects of the Winkler coeffi cient, Pasternak coeffi cient and damping coeffi cient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary diff erential equations with variable coeffi cients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verifi ed through two numerical examples. The infl uences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with diff erent taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam.展开更多
We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles ...We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles are fabricated to optimize the output power and spatial-mode performance. The best devices exhibit single-spatial-mode operation with room-temperature output power up to 350?mW in continuous-wave mode at an emission wavelength around 2.0?μm with a very small far-field lateral divergence angle, which is beyond state of the art in terms of single-spatial-mode output power.展开更多
The flapwise bending vibrational equations of tapered Rayleigh beam are derived based on Hamilton’s principle.The corresponding vibrational characteristics of rotating tapered Rayleigh beams are investigated via vari...The flapwise bending vibrational equations of tapered Rayleigh beam are derived based on Hamilton’s principle.The corresponding vibrational characteristics of rotating tapered Rayleigh beams are investigated via variational iteration method(VIM).Natural frequencies and corresponding mode shapes are examined under various rotation speed,taper ratio and slenderness ratio focusing on two types of tapered beam.The convergence of VIM is examined as part of the paper.Validation of VIM solution is made by referring to results available in other literature and corresponding results show that VIM is capable of yielding precise results in a very efficient way.展开更多
In this paper the semi-analytical analyses of the flexible cantilever tapered functionally graded beam under combined inclined end loading and intermediate loading are studied.In order to derive the fully non-linear e...In this paper the semi-analytical analyses of the flexible cantilever tapered functionally graded beam under combined inclined end loading and intermediate loading are studied.In order to derive the fully non-linear equations governing the non-linear deformation,a curvilinear coordinate system is introduced.A general non-linear second order differential equation that governs the shape of a deflected beam is derived based on the geometric nonlinearities,infinitesimal local displacements and local rotation concepts with remarkable physical properties of functionally graded materials.The solutions obtained from semi-analytical methods are numerically compared with the existing elliptic integral solution for the case of a flexible uniform cantilever functionally graded beam.The effects of taper ratio,inclined end load angle and material property gradient on large deflection of the beam are evaluated.The Adomian decomposition method will be useful toward the design of tapered functionally graded compliant mechanisms driven by smart actuators.展开更多
A tapered rod mounted at one end (base) and subject to a normal force at the other end (tip) is a fundamental structure of continuum mechanics that occurs widely at all size scales from radio towers to fishing rods to...A tapered rod mounted at one end (base) and subject to a normal force at the other end (tip) is a fundamental structure of continuum mechanics that occurs widely at all size scales from radio towers to fishing rods to micro-electromechanical sensors. Although the bending of a uniform rod is well studied and gives rise to mathematical shapes described by elliptic integrals, no exact closed form solution to the nonlinear differential equations of static equilibrium is known for the deflection of a tapered rod. We report in this paper a comprehensive numerical analysis and experimental test of the exact theory of bending deformation of a tapered rod. Given the rod geometry and elastic modulus, the theory yields virtually all the geometric and physical features that an analyst, experimenter, or instrument designer might want as a function of impressed load, such as the exact curve of deformation (termed the elastica), maximum tip displacement, maximum tip deflection angle, distribution of curvature, and distribution of bending moment. Applied experimentally, the theory permits rapid estimation of the elastic modulus of a rod, which is not easily obtainable by other means. We have tested the theory by photographing the shapes of a set of flexible rods of different lengths and tapers subject to a range of impressed loads and using digital image analysis to extract the coordinates of the elastica curves. The extent of flexure in these experiments far exceeded the range of applicability of approximations that linearize the equations of equilibrium or neglect tapering of the rod. Agreement between the measured deflection curves and the exact theoretical predictions was excellent in all but several cases. In these exceptional cases, the nature of the anomalies provided important information regarding the deviation of the rods from an ideal Euler-Bernoulli cantilever, which thereby permitted us to model the deformation of the rods more accurately.展开更多
Broad area semiconductor laser(BAL)has poor lateral beam quality due to lateral mode competition,which limits its application as a high-power optical source.In this work,the distributed Bragg reflector laser diode wit...Broad area semiconductor laser(BAL)has poor lateral beam quality due to lateral mode competition,which limits its application as a high-power optical source.In this work,the distributed Bragg reflector laser diode with tapered grating(TDBR-LD)is studied.By changing the lateral width,the tapered grating increases the loss of high-order lateral modes,thus improving the lateral characteristics of the laser diode.The measuring results show that the TDBR-LD can achieve a single-lobe output under 0.9 A.In contrast to the straight distributed Bragg reflector laser diode(SDBR-LD),the lateral far field divergence of TDBR-LD is measured to be 5.23°at 1 A,representing a 17%decline.The linewidth of TDBR-LD is 0.4 nm at 0.2 A,which is reduced by nearly 43%in comparison with that of SDBR-LD.Meanwhile,both of the devices have a maximum output power value of approximate 470 mW.展开更多
Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low densi...Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.展开更多
频率分集阵列(Frequency Diverse Array, FDA)是作为一种全新的电扫描雷达体制,其方向图所具有的时间-距离-角度三维相关特性在电子对抗和安全通信等领域有广阔的应用前景。一维均匀线性FDA阵列(Uniform Linear Array Frequency Diverse...频率分集阵列(Frequency Diverse Array, FDA)是作为一种全新的电扫描雷达体制,其方向图所具有的时间-距离-角度三维相关特性在电子对抗和安全通信等领域有广阔的应用前景。一维均匀线性FDA阵列(Uniform Linear Array Frequency Diverse Array, ULFDA)的发射方向图存在角度-距离耦合问题,针对这一问题,在对称子阵密度锥削阵结构的基础上,通过正弦频控函数取代原有的均匀线性函数,得到了FDA的点状波束指向控制方法。此外,针对FDA方向图的时变问题,得到了基于子阵结构的密度锥削阵sin-FDA主波束在角度维指向固定、距离维变化时的结论。展开更多
By incorporating the strain gradient elasticity into the classical Bernoulli-Euler beam and Timoshenko beam models, the size-dependent characteristics of wave propaga- tion in micro/nanobeams is studied. The formulati...By incorporating the strain gradient elasticity into the classical Bernoulli-Euler beam and Timoshenko beam models, the size-dependent characteristics of wave propaga- tion in micro/nanobeams is studied. The formulations of dis- persion relation are explicitly derived for both strain gradi- ent beam models, and presented for different material length scale parameters (MLSPs). For both phenomenological size- dependent beam models, the angular frequency, phase veloc- ity and group velocity increase with increasing wave num- ber. However, the velocity ratios approach different values for different beam models, indicating an interesting behavior of the asymptotic velocity ratio. The present theory is also compared with the nonlocal continuum beam models.展开更多
This paper provides innovative and effective instruments for the simplified analysis of serviceability limit states for pitched, kinked, and tapered GLT beams. Specifically, formulas for the evaluation of maximal hori...This paper provides innovative and effective instruments for the simplified analysis of serviceability limit states for pitched, kinked, and tapered GLT beams. Specifically, formulas for the evaluation of maximal horizontal and vertical displacements are derived from a recently-proposed Timoshenko-like non-prismatic beam model. Thereafter, the paper compares the proposed serviceability analysis formulas with other ones available in literature and with highly-refined 2D FE simulations in order to demonstrate the effectiveness of the proposed instruments. The proposed formulas lead to estimations that lie mainly on the conservative side and the errors are smaller than 10% (exceptionally up to 15%) in almost all of the cases of interest for practitioners. Conversely, the accuracy of the proposed formulas decreases for thick and highly-tapered beams since the beam model behind the proposed formulas cannot tackle local effects (like stress concentrations occurring at bearing and beam apex) that significantly influence the beam behavior for such geometries. Finally, the proposed formulas are more accurate than the ones available in literature since the latter ones often provide non-conservative estimations and errors greater than 20% (up to 120%).展开更多
In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental...In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental equation of the element is based on total displacements and is derived under the concept of the quasi-static displacement decomposition. The use of moving support element shows that the element is very simple and convenient to represent continuous beam moving, deforming and vibrating simultaneously due to support motions. The comparison between the numerical results and analytical solutions indicates that the FE result agrees with the analytical solution.展开更多
A new method for sum and difference beam pattern synthesis with low sidelobe is proposed.In the situation of phase taper weighting,it makes use of Fourier transform pair relationship existing between the array factor ...A new method for sum and difference beam pattern synthesis with low sidelobe is proposed.In the situation of phase taper weighting,it makes use of Fourier transform pair relationship existing between the array factor and the element excitations and uses a loop iterative way to derive the array element excitations according to given array factor.The iteration does not stop until the array element excitations meet the initial sidelobe requirements.The method overcomes the defects of traditional methods,such as more searching times,larger amount of calculation and poor robustness.In addition,it can also synthesize the low sidelobe pattern in case of element failures.Simulation verifies the effectiveness of the method.展开更多
This paper focuses on the size-dependently mechanical behaviors of a micro-beam under forced vibration.Governing equations of a micro-beam under forced vibration are established by using the modified couple stress the...This paper focuses on the size-dependently mechanical behaviors of a micro-beam under forced vibration.Governing equations of a micro-beam under forced vibration are established by using the modified couple stress theory,Bernoulli-Euler beam theory and D’Alembert’s principle together.A simply supported micro-beam under forced vibration is solved according to the established governing equations and the method of separation of variables.The dimensionless deflection,amplitude mode and period mode are defined to investigate the size-dependently mechanical behaviors of a micro-beam under forced vibration.Results show that the performance of a micro-beams under forced vibration is distinctly size-dependent when the ratio of micro-beam height to material length-scale parameter is small enough.Both frequency ratio and loading location are the important factors that determine the sizedependent performance of a micro-beams under forced vibration.展开更多
The study adopts the variational method for analyzing the cantilever tapered beams under a tip load as well as a definite end displacement,and further determining the optimized shapes and materials that can minimize t...The study adopts the variational method for analyzing the cantilever tapered beams under a tip load as well as a definite end displacement,and further determining the optimized shapes and materials that can minimize the weights.Two types of beams are taken into account,i.e.,the Euler-Bernoulli beam without considering shear deformation and the Timoshenko beam with shear deformation.By using the energy theorem and the reference of isoperimetric problem,the width variation curves and the corresponding minimum masses are derived for both beam types.The optimized curve of beam width for the Euler-Bernoulli beam is found to be a linear function,but nonlinear for the Timoshenko beam.It is also found that the optimized curve in the Timoshenko beam case starts from non-zero at the tip end,but its tendency gradually approaches the one of the Euler-Bernoulli beam.The results indicate that with the increase of the Poisson’s ratio,the required minimum mass of the beam will increase no matter how the material changes,suggesting that the optimized mass for the case of Euler-Bernoulli beam is the lower boundary limit which the Timoshenko case cannot go beyond.Furthermore,the ratio r/E(density against Elastic Modulus)of the material should be as small as possible,while the ratio h2/L4 of the beam should be as large as possible in order to minimize the mass for the case of Euler-Bernoulli beam,of which the conclusion is extended to be applicable for the case of Timoshenko beam.In addition,the optimized curves for Euler-Bernoulli beam types are all found to be power functions of length for both tip point load cases and uniform load cases.展开更多
基金AHKJT of China under Grant Nos.1708085QE121 and 1808085ME147AHEDU of China under Grant No.TSKJ2017B13
文摘The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the eff ects of the Winkler coeffi cient, Pasternak coeffi cient and damping coeffi cient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary diff erential equations with variable coeffi cients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verifi ed through two numerical examples. The infl uences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with diff erent taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam.
基金Supported by the National Basic Research Program of China under Grant Nos 2014CB643903 and 2013CB932904the National Natural Science Foundation of China under Grant Nos 61435012 and 61290303the Strategic Priority Research Program(B) of the Chinese Academy of Sciences under Grant No XDB01010200
文摘We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles are fabricated to optimize the output power and spatial-mode performance. The best devices exhibit single-spatial-mode operation with room-temperature output power up to 350?mW in continuous-wave mode at an emission wavelength around 2.0?μm with a very small far-field lateral divergence angle, which is beyond state of the art in terms of single-spatial-mode output power.
基金the National Natural Science Foundation of China(Grant Nos.51779265 and 52171285)Open Project Program of State Key Laboratory of Structural Analysis for Industrial Equipment(Grant No.GZ19119)+3 种基金Science Foundation of China University of Petroleum,Beijing(Grant No.2462020YXZZ045)Open Project Program of Beijing Key Laboratory of Pipeline Critical Technology and Equipment for Deepwater Oil&Gas Development(Grant No.BIPT2018002)Special Funding for Promoting Economic Development in Guangdong Province(Grant No.GDOE[2019]A39)Opening fund of State Key Laboratory of Hydraulic Engineering Simulation and Safety(Grant No.HESS-1411)。
文摘The flapwise bending vibrational equations of tapered Rayleigh beam are derived based on Hamilton’s principle.The corresponding vibrational characteristics of rotating tapered Rayleigh beams are investigated via variational iteration method(VIM).Natural frequencies and corresponding mode shapes are examined under various rotation speed,taper ratio and slenderness ratio focusing on two types of tapered beam.The convergence of VIM is examined as part of the paper.Validation of VIM solution is made by referring to results available in other literature and corresponding results show that VIM is capable of yielding precise results in a very efficient way.
文摘In this paper the semi-analytical analyses of the flexible cantilever tapered functionally graded beam under combined inclined end loading and intermediate loading are studied.In order to derive the fully non-linear equations governing the non-linear deformation,a curvilinear coordinate system is introduced.A general non-linear second order differential equation that governs the shape of a deflected beam is derived based on the geometric nonlinearities,infinitesimal local displacements and local rotation concepts with remarkable physical properties of functionally graded materials.The solutions obtained from semi-analytical methods are numerically compared with the existing elliptic integral solution for the case of a flexible uniform cantilever functionally graded beam.The effects of taper ratio,inclined end load angle and material property gradient on large deflection of the beam are evaluated.The Adomian decomposition method will be useful toward the design of tapered functionally graded compliant mechanisms driven by smart actuators.
文摘A tapered rod mounted at one end (base) and subject to a normal force at the other end (tip) is a fundamental structure of continuum mechanics that occurs widely at all size scales from radio towers to fishing rods to micro-electromechanical sensors. Although the bending of a uniform rod is well studied and gives rise to mathematical shapes described by elliptic integrals, no exact closed form solution to the nonlinear differential equations of static equilibrium is known for the deflection of a tapered rod. We report in this paper a comprehensive numerical analysis and experimental test of the exact theory of bending deformation of a tapered rod. Given the rod geometry and elastic modulus, the theory yields virtually all the geometric and physical features that an analyst, experimenter, or instrument designer might want as a function of impressed load, such as the exact curve of deformation (termed the elastica), maximum tip displacement, maximum tip deflection angle, distribution of curvature, and distribution of bending moment. Applied experimentally, the theory permits rapid estimation of the elastic modulus of a rod, which is not easily obtainable by other means. We have tested the theory by photographing the shapes of a set of flexible rods of different lengths and tapers subject to a range of impressed loads and using digital image analysis to extract the coordinates of the elastica curves. The extent of flexure in these experiments far exceeded the range of applicability of approximations that linearize the equations of equilibrium or neglect tapering of the rod. Agreement between the measured deflection curves and the exact theoretical predictions was excellent in all but several cases. In these exceptional cases, the nature of the anomalies provided important information regarding the deviation of the rods from an ideal Euler-Bernoulli cantilever, which thereby permitted us to model the deformation of the rods more accurately.
基金Project supported by theScienceand Technology Development Plan of Jilin Province,China(Grant Nos.20210201030GX and 20210201089GX).
文摘Broad area semiconductor laser(BAL)has poor lateral beam quality due to lateral mode competition,which limits its application as a high-power optical source.In this work,the distributed Bragg reflector laser diode with tapered grating(TDBR-LD)is studied.By changing the lateral width,the tapered grating increases the loss of high-order lateral modes,thus improving the lateral characteristics of the laser diode.The measuring results show that the TDBR-LD can achieve a single-lobe output under 0.9 A.In contrast to the straight distributed Bragg reflector laser diode(SDBR-LD),the lateral far field divergence of TDBR-LD is measured to be 5.23°at 1 A,representing a 17%decline.The linewidth of TDBR-LD is 0.4 nm at 0.2 A,which is reduced by nearly 43%in comparison with that of SDBR-LD.Meanwhile,both of the devices have a maximum output power value of approximate 470 mW.
基金Project(2011-0006548)supported by Basic Science Research Program through the National Research Foundation of Korea
文摘Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.
文摘频率分集阵列(Frequency Diverse Array, FDA)是作为一种全新的电扫描雷达体制,其方向图所具有的时间-距离-角度三维相关特性在电子对抗和安全通信等领域有广阔的应用前景。一维均匀线性FDA阵列(Uniform Linear Array Frequency Diverse Array, ULFDA)的发射方向图存在角度-距离耦合问题,针对这一问题,在对称子阵密度锥削阵结构的基础上,通过正弦频控函数取代原有的均匀线性函数,得到了FDA的点状波束指向控制方法。此外,针对FDA方向图的时变问题,得到了基于子阵结构的密度锥削阵sin-FDA主波束在角度维指向固定、距离维变化时的结论。
基金supported by the National Natural Science Foundation of China(11202117,11272186,11172231 and 50928601)the Postdoctoral Science Foundation of China(2012M521326)+3 种基金the Natural Science Fund of Shandong Province(ZR2012AM014 and BS2012ZZ006)Independent Innovation Fund of Shandong University(2011GN055)National Science Foundation(CMMI-0643726),DARPA(W91CRB-11-C-0112)Changjiang Scholar Program from Ministry of Education of China
文摘By incorporating the strain gradient elasticity into the classical Bernoulli-Euler beam and Timoshenko beam models, the size-dependent characteristics of wave propaga- tion in micro/nanobeams is studied. The formulations of dis- persion relation are explicitly derived for both strain gradi- ent beam models, and presented for different material length scale parameters (MLSPs). For both phenomenological size- dependent beam models, the angular frequency, phase veloc- ity and group velocity increase with increasing wave num- ber. However, the velocity ratios approach different values for different beam models, indicating an interesting behavior of the asymptotic velocity ratio. The present theory is also compared with the nonlocal continuum beam models.
文摘This paper provides innovative and effective instruments for the simplified analysis of serviceability limit states for pitched, kinked, and tapered GLT beams. Specifically, formulas for the evaluation of maximal horizontal and vertical displacements are derived from a recently-proposed Timoshenko-like non-prismatic beam model. Thereafter, the paper compares the proposed serviceability analysis formulas with other ones available in literature and with highly-refined 2D FE simulations in order to demonstrate the effectiveness of the proposed instruments. The proposed formulas lead to estimations that lie mainly on the conservative side and the errors are smaller than 10% (exceptionally up to 15%) in almost all of the cases of interest for practitioners. Conversely, the accuracy of the proposed formulas decreases for thick and highly-tapered beams since the beam model behind the proposed formulas cannot tackle local effects (like stress concentrations occurring at bearing and beam apex) that significantly influence the beam behavior for such geometries. Finally, the proposed formulas are more accurate than the ones available in literature since the latter ones often provide non-conservative estimations and errors greater than 20% (up to 120%).
文摘In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental equation of the element is based on total displacements and is derived under the concept of the quasi-static displacement decomposition. The use of moving support element shows that the element is very simple and convenient to represent continuous beam moving, deforming and vibrating simultaneously due to support motions. The comparison between the numerical results and analytical solutions indicates that the FE result agrees with the analytical solution.
基金Sponsored by the National Nature Science Foundation of China(60972152)
文摘A new method for sum and difference beam pattern synthesis with low sidelobe is proposed.In the situation of phase taper weighting,it makes use of Fourier transform pair relationship existing between the array factor and the element excitations and uses a loop iterative way to derive the array element excitations according to given array factor.The iteration does not stop until the array element excitations meet the initial sidelobe requirements.The method overcomes the defects of traditional methods,such as more searching times,larger amount of calculation and poor robustness.In addition,it can also synthesize the low sidelobe pattern in case of element failures.Simulation verifies the effectiveness of the method.
基金The authors of this paper acknowledge the supports from the National Key Research and Development Program of China(Grant No.2017YFC0307604)the Talent Foundation of China University of Petroleum(Grant No.Y1215042).
文摘This paper focuses on the size-dependently mechanical behaviors of a micro-beam under forced vibration.Governing equations of a micro-beam under forced vibration are established by using the modified couple stress theory,Bernoulli-Euler beam theory and D’Alembert’s principle together.A simply supported micro-beam under forced vibration is solved according to the established governing equations and the method of separation of variables.The dimensionless deflection,amplitude mode and period mode are defined to investigate the size-dependently mechanical behaviors of a micro-beam under forced vibration.Results show that the performance of a micro-beams under forced vibration is distinctly size-dependent when the ratio of micro-beam height to material length-scale parameter is small enough.Both frequency ratio and loading location are the important factors that determine the sizedependent performance of a micro-beams under forced vibration.
基金supports from Xi’an Jiaotong–Liverpool University(RDF 14-02-44,RDF 15-01-38,RDF 18-01-23 and PGRS1906002)the Key Program Special Fund at XJTLU(Grant No.KSF-E-19)are gratefully acknowledged.
文摘The study adopts the variational method for analyzing the cantilever tapered beams under a tip load as well as a definite end displacement,and further determining the optimized shapes and materials that can minimize the weights.Two types of beams are taken into account,i.e.,the Euler-Bernoulli beam without considering shear deformation and the Timoshenko beam with shear deformation.By using the energy theorem and the reference of isoperimetric problem,the width variation curves and the corresponding minimum masses are derived for both beam types.The optimized curve of beam width for the Euler-Bernoulli beam is found to be a linear function,but nonlinear for the Timoshenko beam.It is also found that the optimized curve in the Timoshenko beam case starts from non-zero at the tip end,but its tendency gradually approaches the one of the Euler-Bernoulli beam.The results indicate that with the increase of the Poisson’s ratio,the required minimum mass of the beam will increase no matter how the material changes,suggesting that the optimized mass for the case of Euler-Bernoulli beam is the lower boundary limit which the Timoshenko case cannot go beyond.Furthermore,the ratio r/E(density against Elastic Modulus)of the material should be as small as possible,while the ratio h2/L4 of the beam should be as large as possible in order to minimize the mass for the case of Euler-Bernoulli beam,of which the conclusion is extended to be applicable for the case of Timoshenko beam.In addition,the optimized curves for Euler-Bernoulli beam types are all found to be power functions of length for both tip point load cases and uniform load cases.