The optimum shape of a two-dimensional undulatory plate in its motion in fluid flow is analyzed and the physical parameters（the thrust and the power）are calculated by the boundary element method.With the commonly us...The optimum shape of a two-dimensional undulatory plate in its motion in fluid flow is analyzed and the physical parameters（the thrust and the power）are calculated by the boundary element method.With the commonly used Lagrange multiplier method,only a saddle point of the optimum solution can be obtained,but not the solution itself due to the singularity of the problem.To eliminate the singularity,a method is proposed by adding an amplitude constraint.The new method is a generalization of that proposed by Wu,and it can be applied to more complex cases.The optimum shape of the linearly varying amplitude motion is studied in detail.It is shown that both the maximum and the minimum solutions exist when the frequency is higher than a critical value.For a high frequency,the maximum efficient motion with a large amplitude at the leading edge and a small amplitude at the trailing edge induces a large leading edge suction force.As the frequency decreases,the leading edge suction force decreases to a minimum and then increases.For high wavenumbers,there exists an optimum frequency with the maximum efficiency.High efficiency holds over a large range of frequency.The optimum efficiency increases as the wavenumber increases.The increase of the wavenumber can also reduce the leading edge suction force.The optimization method can also be applied to a quadratically varying amplitude motion.It is found that the optimum efficiency is larger than that for the linearly varying amplitude motion.However,the additional efficiency is relatively small,especially as the original efficiency is already high enough.展开更多
The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be g...The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.展开更多
A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the ...A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the invisible modes, and therefore the commonly used Lagrange multiplier method cannot predict an optimum solution but just a saddle point. To eliminate the singularity, an additional amplitude inequality constraint is added to the problem. A numerical optimization code with a sequential quadratic programming method is used to solve the problem. The method is applied to several cases of the motion of two-dimensional and three-dimensional undulatory plates, and the optimum results are obtained.展开更多
In the present paper, the effect of a small bottom tmdulation of the sea bed in the form of periodic bed form on the surface waves generated due to a rolling oscillation of a vertical barrier either partially immersed...In the present paper, the effect of a small bottom tmdulation of the sea bed in the form of periodic bed form on the surface waves generated due to a rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of non uniform finite depth is investigated. A simplified perturbation technique involving a non dimensional parameter characterizing the smallness of the bottom deformation is applied to reduce the given boundary value problem to two independent boundary value problems upto first order. The first boundary value problem corresponds to the problem of water wave generation due to rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of uniform finite depth. This is a well known problem whose solution is available in the literature. From the second boundary value problem, the first order correction to the wave amplitude at infinity is evaluated in terms of the shape function characterizing the bottom undulation, by employing Green＇s integral theorem. For a patch of sinusoidal ripples at the sea bottom, the first order correction to the wave amplitude at infinity for both the configuration of the barrier is then evaluated numerically and illustrated graphically for various values of the wave number. It is observed that resonant interaction of the wave generated, with the sinusoidal bottom undulation occurs when the ratio of twice the wavelength of the sinusoidal ripple to the wave length of waves generated, approaches unity. Also it is found that the resonance increases as the length of the barrier increases.展开更多
It is difficult to quantitatively detect defects by using the time domain or frequency domain features of Lamb wave signals due to their dispersion and multimodal characteristics.Therefore,it is important to discover ...It is difficult to quantitatively detect defects by using the time domain or frequency domain features of Lamb wave signals due to their dispersion and multimodal characteristics.Therefore,it is important to discover an intrinsical parameter of Lamb waves that could be used as a damage sensitive feature.In this paper,quantitative defect detection in aluminium plates is carried out by means of wavenumber analysis approach.The wavenumber of excited Lamb wave mode is a fixed value,given a frequency,a thickness and material properties of the target plate.When Lamb waves propagate to the structural discontinuity,new wavenumber components are created by abrupt wavefield change.The new wavenumber components can be identified in the frequency-wavenumber domain.To estimate spatially dependent wavenumber values,a short-space two-dimensional Fourier transform(FT)method is presented for processing wavefield data of Lamb waves.The results can be used to determine the location,size and depth of rectangular notch.The analysis techniques are demonstrated using simulation examples of an aluminium plate with a rectangular notch.Then,the wavenumber analysis method is applied to simulation data that are obtained through a range of notch depths and widths.The results are analyzed and rules of the technique with regards to estimating notch depth are determined.Based on simulation results,guidelines for using the technique are developed.Finally,experimental wavefield data are obtained in aluminium plates with rectangular notches by a full noncontact transceiving method,i.e.,laser-laser method.Band-pass filtering combined with continuous wavelet transform is used to extract a certain frequency component from the full laser-induced wavefield with wide band.Shortspace two-dimensional FT method is used for further processing full wavefield data at a certain frequency to estimate spatially dependent wavenumber values.The consistency of simulation and experimental results shows the effectiveness of proposed wavenumber method for quantitative rectangular notch detection.展开更多
Some theorems of compactly supported non-tensor product form two-dimension Daubechies wavelet were analysed carefully. Compactly supported non-tensor product form two-dimension wavelet was constructed, then non-tensor...Some theorems of compactly supported non-tensor product form two-dimension Daubechies wavelet were analysed carefully. Compactly supported non-tensor product form two-dimension wavelet was constructed, then non-tensor product form two dimension wavelet finite element was used to solve the deflection problem of elastic thin plate. The error order was researched. A numerical example was given at last.展开更多
Two-dimensional （2D） equations for multiferroic （MF） laminated plates with imperfect interfaces are established in this paper. The interface between two adjacent sublayers, which are not perfectly bonded together,...Two-dimensional （2D） equations for multiferroic （MF） laminated plates with imperfect interfaces are established in this paper. The interface between two adjacent sublayers, which are not perfectly bonded together, is modeled as a general spring-type layer. The mechanical displacements, and the electric and magnetic potentials of the two adjacent layers are assumed to be discontinuous at the interface. As an example, the influences of imperfect interfaces on the magnetoelectric （ME） coupling effects in an MF sandwich plate are investigated with the established 2D governing equations. Numerical results show that the imperfect interfaces have a significant impact on the ME coupling effects in MF laminated structures.展开更多
Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of th...Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate,thereby impacting stability.Through a combination of theoretical analysis,mechanical testing,and numerical simulations,this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics.This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate,which was validated through numerical simulations.The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples,with the undulation height exerting a more pronounced effect.The strength of the samples with undulating surfaces is approximately 50%-60% that of the samples with flat surfaces.The failure mode under uniaxial compression is predominantly tensile,resulting in long and slender block fragments with a characteristic“Ⅲ”-shaped tensile fracture pattern.During the loading process,samples with undu-lating surfaces dissipate energy at all stages,with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks.The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate.Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength.This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.展开更多
This study evaluates the physical mechanisms of incident waves as they interact with a porous wavy barrier of finite thickness.A wave-trapping chamber is formed between the thick wavy barrier(TWB)and partially reflect...This study evaluates the physical mechanisms of incident waves as they interact with a porous wavy barrier of finite thickness.A wave-trapping chamber is formed between the thick wavy barrier(TWB)and partially reflecting seawall(PRS).The effect of seabed undulations is incorporated into the wave-trapping analysis of the TWB.The boundary value problem proposed in this study is solved using a multidomain boundary element method within the context of linear potential flow theory.Coefficients such as reflection,runup,horizontal force on PRS,and vertical force on TWB are examined for various structural configurations.The position of seabed undulations is analyzed for four scenarios:i)seabed undulations upwave of the wavy barrier with a trapping chamber,ii)seabed undulations upwave of the wavy barrier without a trapping chamber,iii)seabed undulations underneath the wavy barrier with a trapping chamber,and iv)seabed undulations beneath the wavy barrier without a trapping chamber.The study results are compared with known results to verify their accuracy.The effects of PRS,TWB porosity,trapping chamber,plate thickness,seabed type,and submergence depth on hydrodynamic coefficients are analyzed against relative water depth.The study reveals that the introduction of a porous TWB with a trapping chamber results in minimal hydrodynamic coefficients(reduced reflection and force on a wall)compared to a rigid TWB without a trapping chamber.A comparison of various seabeds is reported for all combinations of TWB with a chamber.The sloping seabed upwave of the barrier with a trapping chamber,20%plate porosity,and 50%wall reflection at an appropriate submergence depth could replace gravity-type breakwaters in deeper waters.This study holds great potential for analyzing wave trapping coefficients by TWB to provide an effective coastal protection system.展开更多
Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimiz...Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimized during the structural design stage.Purpose Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.In the HEPS undulator design and manufacturing stage,it is found that under special circumstances,such as after the height of the feet is adjusted,or after the undulator is lifted to other place,the base plate and girder may deform more than expected.Methods Therefore based on ANSYS simulation and experimental test results,the factors causing the deformation of the girders are carefully analyzed.Base plate and feet were optimized for different types of undulators to avoid girder deformation.Related simulation and laser tracker measurement were performed tofind out the reason in this paper.Results and conclusion Results show that the base plate of C-frame undulators will collapse and deform under the action of magnetic force.Asymmetric sagged base plate is the main reason of girder deformation.Increasing the thickness of the base plate and increasing the number of feet can both reduce that deformation.Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.展开更多
基金Project supported by the 111 Project of China (Grant No. B07033)
文摘The optimum shape of a two-dimensional undulatory plate in its motion in fluid flow is analyzed and the physical parameters（the thrust and the power）are calculated by the boundary element method.With the commonly used Lagrange multiplier method,only a saddle point of the optimum solution can be obtained,but not the solution itself due to the singularity of the problem.To eliminate the singularity,a method is proposed by adding an amplitude constraint.The new method is a generalization of that proposed by Wu,and it can be applied to more complex cases.The optimum shape of the linearly varying amplitude motion is studied in detail.It is shown that both the maximum and the minimum solutions exist when the frequency is higher than a critical value.For a high frequency,the maximum efficient motion with a large amplitude at the leading edge and a small amplitude at the trailing edge induces a large leading edge suction force.As the frequency decreases,the leading edge suction force decreases to a minimum and then increases.For high wavenumbers,there exists an optimum frequency with the maximum efficiency.High efficiency holds over a large range of frequency.The optimum efficiency increases as the wavenumber increases.The increase of the wavenumber can also reduce the leading edge suction force.The optimization method can also be applied to a quadratically varying amplitude motion.It is found that the optimum efficiency is larger than that for the linearly varying amplitude motion.However,the additional efficiency is relatively small,especially as the original efficiency is already high enough.
文摘The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.
文摘A numerical method for the optimum motion of an undulatory swimming plate is presented. The optimum problem is stated as minimizing the power input under the condition of fixed thrust. The problem is singular for the invisible modes, and therefore the commonly used Lagrange multiplier method cannot predict an optimum solution but just a saddle point. To eliminate the singularity, an additional amplitude inequality constraint is added to the problem. A numerical optimization code with a sequential quadratic programming method is used to solve the problem. The method is applied to several cases of the motion of two-dimensional and three-dimensional undulatory plates, and the optimum results are obtained.
基金Supported by DST through the Research Project No.SR/SY/MS: 521/08
文摘In the present paper, the effect of a small bottom tmdulation of the sea bed in the form of periodic bed form on the surface waves generated due to a rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of non uniform finite depth is investigated. A simplified perturbation technique involving a non dimensional parameter characterizing the smallness of the bottom deformation is applied to reduce the given boundary value problem to two independent boundary value problems upto first order. The first boundary value problem corresponds to the problem of water wave generation due to rolling oscillation of a vertical barrier either partially immersed or completely submerged in water of uniform finite depth. This is a well known problem whose solution is available in the literature. From the second boundary value problem, the first order correction to the wave amplitude at infinity is evaluated in terms of the shape function characterizing the bottom undulation, by employing Green＇s integral theorem. For a patch of sinusoidal ripples at the sea bottom, the first order correction to the wave amplitude at infinity for both the configuration of the barrier is then evaluated numerically and illustrated graphically for various values of the wave number. It is observed that resonant interaction of the wave generated, with the sinusoidal bottom undulation occurs when the ratio of twice the wavelength of the sinusoidal ripple to the wave length of waves generated, approaches unity. Also it is found that the resonance increases as the length of the barrier increases.
基金supported by the National Natural Science Foundation of China(Nos.51475012,11772014,and 11272021)
文摘It is difficult to quantitatively detect defects by using the time domain or frequency domain features of Lamb wave signals due to their dispersion and multimodal characteristics.Therefore,it is important to discover an intrinsical parameter of Lamb waves that could be used as a damage sensitive feature.In this paper,quantitative defect detection in aluminium plates is carried out by means of wavenumber analysis approach.The wavenumber of excited Lamb wave mode is a fixed value,given a frequency,a thickness and material properties of the target plate.When Lamb waves propagate to the structural discontinuity,new wavenumber components are created by abrupt wavefield change.The new wavenumber components can be identified in the frequency-wavenumber domain.To estimate spatially dependent wavenumber values,a short-space two-dimensional Fourier transform(FT)method is presented for processing wavefield data of Lamb waves.The results can be used to determine the location,size and depth of rectangular notch.The analysis techniques are demonstrated using simulation examples of an aluminium plate with a rectangular notch.Then,the wavenumber analysis method is applied to simulation data that are obtained through a range of notch depths and widths.The results are analyzed and rules of the technique with regards to estimating notch depth are determined.Based on simulation results,guidelines for using the technique are developed.Finally,experimental wavefield data are obtained in aluminium plates with rectangular notches by a full noncontact transceiving method,i.e.,laser-laser method.Band-pass filtering combined with continuous wavelet transform is used to extract a certain frequency component from the full laser-induced wavefield with wide band.Shortspace two-dimensional FT method is used for further processing full wavefield data at a certain frequency to estimate spatially dependent wavenumber values.The consistency of simulation and experimental results shows the effectiveness of proposed wavenumber method for quantitative rectangular notch detection.
文摘Some theorems of compactly supported non-tensor product form two-dimension Daubechies wavelet were analysed carefully. Compactly supported non-tensor product form two-dimension wavelet was constructed, then non-tensor product form two dimension wavelet finite element was used to solve the deflection problem of elastic thin plate. The error order was researched. A numerical example was given at last.
基金supported by the National Natural Science Foundation of China(11672265,11202182,11272281,11621062,and 11321202)the Fundamental Research Funds for the Central Universities(2016QNA4026 and 2016XZZX001-05)the open foundation of Zhejiang Provincial Top Key Discipline of Mechanical Engineering
文摘Two-dimensional （2D） equations for multiferroic （MF） laminated plates with imperfect interfaces are established in this paper. The interface between two adjacent sublayers, which are not perfectly bonded together, is modeled as a general spring-type layer. The mechanical displacements, and the electric and magnetic potentials of the two adjacent layers are assumed to be discontinuous at the interface. As an example, the influences of imperfect interfaces on the magnetoelectric （ME） coupling effects in an MF sandwich plate are investigated with the established 2D governing equations. Numerical results show that the imperfect interfaces have a significant impact on the ME coupling effects in MF laminated structures.
基金the National Key Research and Development Program of China(Nos.2023YFC2907501 and 2023YFC2907503)the National Natural Science Foundation of China(Nos.52374106 and 52274154)the Fundamental Research Funds for the Central Universities(No.2023YQTD02).
文摘Coal wall stability is a critical factor influencing coal mining efficiency and threatens the safety of working faces,where irregular coal wall surfaces significantly affect the contact and support effectiveness of the support plate,thereby impacting stability.Through a combination of theoretical analysis,mechanical testing,and numerical simulations,this study establishes a mechanical model of irregular coal wall surfaces to investigate the effects of the undulation period and undulation height on coal wall failure characteristics.This research reveals the mechanical response mechanisms of irregular coal wall surfaces and proposes an innovative method to enhance coal wall stability by improving the supporting cushion material of the support plate,which was validated through numerical simulations.The results show that the undulation height and undulation period significantly influence the macroscopic mechanical parameters of the samples,with the undulation height exerting a more pronounced effect.The strength of the samples with undulating surfaces is approximately 50%-60% that of the samples with flat surfaces.The failure mode under uniaxial compression is predominantly tensile,resulting in long and slender block fragments with a characteristic“Ⅲ”-shaped tensile fracture pattern.During the loading process,samples with undu-lating surfaces dissipate energy at all stages,with a greater proportion of energy dissipation occurring during the early loading stage because of structural damage and the formation of internal cracks.The surface compressive and tensile stresses are correlated with the curvature radius of the convex surface and the elastic modulus of the supporting plate.Reducing the elastic modulus of the supporting plate material can effectively alleviate the stress concentration at convex locations and increase the peak strength.This study provides theoretical foundations and technical references for the prevention and control of coal wall spalling in deep thick coal seam mining.
文摘This study evaluates the physical mechanisms of incident waves as they interact with a porous wavy barrier of finite thickness.A wave-trapping chamber is formed between the thick wavy barrier(TWB)and partially reflecting seawall(PRS).The effect of seabed undulations is incorporated into the wave-trapping analysis of the TWB.The boundary value problem proposed in this study is solved using a multidomain boundary element method within the context of linear potential flow theory.Coefficients such as reflection,runup,horizontal force on PRS,and vertical force on TWB are examined for various structural configurations.The position of seabed undulations is analyzed for four scenarios:i)seabed undulations upwave of the wavy barrier with a trapping chamber,ii)seabed undulations upwave of the wavy barrier without a trapping chamber,iii)seabed undulations underneath the wavy barrier with a trapping chamber,and iv)seabed undulations beneath the wavy barrier without a trapping chamber.The study results are compared with known results to verify their accuracy.The effects of PRS,TWB porosity,trapping chamber,plate thickness,seabed type,and submergence depth on hydrodynamic coefficients are analyzed against relative water depth.The study reveals that the introduction of a porous TWB with a trapping chamber results in minimal hydrodynamic coefficients(reduced reflection and force on a wall)compared to a rigid TWB without a trapping chamber.A comparison of various seabeds is reported for all combinations of TWB with a chamber.The sloping seabed upwave of the barrier with a trapping chamber,20%plate porosity,and 50%wall reflection at an appropriate submergence depth could replace gravity-type breakwaters in deeper waters.This study holds great potential for analyzing wave trapping coefficients by TWB to provide an effective coastal protection system.
文摘Background Nineteen undulators of various types are being fabricated for high-energy photon source(HEPS).In order to ensure the optical performance of the undulators,the girder deformation is usually carefully optimized during the structural design stage.Purpose Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.In the HEPS undulator design and manufacturing stage,it is found that under special circumstances,such as after the height of the feet is adjusted,or after the undulator is lifted to other place,the base plate and girder may deform more than expected.Methods Therefore based on ANSYS simulation and experimental test results,the factors causing the deformation of the girders are carefully analyzed.Base plate and feet were optimized for different types of undulators to avoid girder deformation.Related simulation and laser tracker measurement were performed tofind out the reason in this paper.Results and conclusion Results show that the base plate of C-frame undulators will collapse and deform under the action of magnetic force.Asymmetric sagged base plate is the main reason of girder deformation.Increasing the thickness of the base plate and increasing the number of feet can both reduce that deformation.Optimization of magnet girder deformation is one of the key points to ensure undulator magneticfield performance.To reduce magnet girder deformation,base plate,feet and strong back should be designed carefully.
