A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversi...A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversion.In this study,the nodal quadrature method is employed to construct a lumped mass matrix for the Chebyshev spectral element method(CSEM).A Gauss-Lobatto type quadrature,based on Gauss-Lobatto-Chebyshev points with a weighting function of unity,is thus derived.With the aid of this quadrature,the CSEM can take advantage of explicit time-marching schemes and provide an efficient new tool for solving structural dynamic problems.Several types of lumped mass Chebyshev spectral elements are designed,including rod,beam and plate elements.The performance of the developed method is examined via some numerical examples of natural vibration and elastic wave propagation,accompanied by their comparison to that of traditional consistent-mass CSEM or the classical finite element method(FEM).Numerical results indicate that the proposed method displays comparable accuracy as its consistent-mass counterpart,and is more accurate than classical FEM.For the simulation of elastic wave propagation in structures induced by high-frequency loading,this method achieves satisfactory performance in accuracy and efficiency.展开更多
From the Boltzmann's constitutive law of viscoelastic materials and the linear theory of elastic materials with voids, a constitutive model of generalized force fields for viscoelastic solids with voids was given....From the Boltzmann's constitutive law of viscoelastic materials and the linear theory of elastic materials with voids, a constitutive model of generalized force fields for viscoelastic solids with voids was given. By using the variational integral method, the convolution-type functional was given and the corresponding generalized variational principles and potential energy principle of viscoelastic solids with voids were presented. It can be shown that the variational principles correspond to the differential equations and the initial and boundary conditions of viscoelastic body with voids. As an application, a generalized variational principle of viscoelastic Timoshenko beams with damage was obtained which corresponds to the differential equations of generalized motion and the initial and boundary conditions of beams. The variational principles provide a way for solving problems of viscoelastic solids with voids.展开更多
Decorative wood panels containing pouches of bio-based phase changing materials(PCMs) were prepared. Three different PCM mixtures were used: a blend of capric and lauric acids as well as two commercial products, Puret...Decorative wood panels containing pouches of bio-based phase changing materials(PCMs) were prepared. Three different PCM mixtures were used: a blend of capric and lauric acids as well as two commercial products, Puretemp?20 and Puretemp?23(Puretemp). The panels consist of engraved Medium Density Fiberboard(MDF) filled with a plastic pouch filled with PCM. High density fiberboard(HDF) was used on top of the panels to enclose the PCM pouches. PCM mixtures were first tested by differential scanning calorimetry(DSC). Phase change temperature and total heat storage of the panels were measured for both fusion and solidification with a Dynamic Heat-Flow Meter Apparatus(DHFMA). DSC and DHFMA results were compared, allowing a better understanding of results gathered from these two techniques. DSC calibration has been revealed important when assessing PCMs. The panels present a phase change temperature and a latent heat storage suitable for buildings applications. The panel made with Puretemp?23 presented the highest energy, with 57.1 J g^(-1). Thermal cycling was conducted on the panels to investigate thermal reliability, which revealed small modifications of thermal properties for two products. For all cases, latent heat was found stable. Hygro-mechanical behavior of the panels was also evaluated as these where designed to be esthetic decorative panels. This study exposes the potential of a new type of wood-based panels loaded with PCM for thermal energy storage and brings overall knowledge about PCM products thermal characterization.展开更多
Product system design is a mature concept in western developed countries. It has been applied in war industry during the last century. However,up until now,functional combination is still the main method for product s...Product system design is a mature concept in western developed countries. It has been applied in war industry during the last century. However,up until now,functional combination is still the main method for product system de-sign in China. Therefore,in terms of a concept of product generation and product interaction we are in a weak position compared with the requirements of global markets. Today,the idea of serial product design has attracted much attention in the design field and the definition of product generation as well as its parameters has already become the standard in serial product designs. Although the design of a large-scale NC machine tool is complicated,it can be further optimized by the precise exercise of object design by placing the concept of platform establishment firmly into serial product de-sign. The essence of a serial product design has been demonstrated by the design process of a large-scale NC machine tool.展开更多
In this article,several spectral models describing the stationary stochastic process of earthquake ground motion are explored and compared.The Hu-Zhou spectrum,which is regarded as an improved model of the Kanai-Tajim...In this article,several spectral models describing the stationary stochastic process of earthquake ground motion are explored and compared.The Hu-Zhou spectrum,which is regarded as an improved model of the Kanai-Tajimi spectrum,is concerned.It is proven that the earthquake-induced ground acceleration process described by the Hu-Zhou spectrum is a twice filtered white noise process in essence,and two filters for modifying low-frequency components and moderate-and high-frequency components respectively are investigated.A total of 1946 strong earthquake records at different sites were employed to determine the parameters of spectral models,including the Kanai-Tajimi spectrum,the Clough-Penzien spectrum and the Hu-Zhou spectrum.The results showed that the Hu-Zhou spectrum fits well with the actual observed ground motions over the whole frequency range,and that it is not only distinct in physical meaning and concise in mathematical expression,but also reasonable in practice.展开更多
Control of the directional bounce of droplets impacting solid surfaces is crucial for many agricultural and industrial applications.However,for the universal impact process of raindrops on plant leaves,little is known...Control of the directional bounce of droplets impacting solid surfaces is crucial for many agricultural and industrial applications.However,for the universal impact process of raindrops on plant leaves,little is known about how the highly coupled and complicated fluid–structure interaction controls the postimpact motion of droplets and endows the leaves with tenacious vitality.Here,we report a leaf-like superhydrophobic cantilever to flexibly bounce droplets with well-defined directionality and controllability.Through theoretical modeling and three-dimensional fluid–solid coupling simulations,we find that the flexible cantilever significantly relieves the impacting forces of raindrops to reduce droplet fragmentation and enhance water repellency.The results further uncover the scaling relations of the droplet bouncing direction with respect to Weber number and cantilever stiffness.By this technique,the seemed disorganized postimpact movements of droplets are programmable and predictable,achieving the goal of where to point and where to hit automatically.This work advances the understanding of natural droplet impact phenomena,opens a new avenue for delicately controlling liquid motion in space with soft materials,and inspires a plethora of applications like soft robots to transport materials and energies,monitor plant growth as well as predict pathogen transmission in plants.展开更多
Based on the mechanics of material,the bending stiffness and intensity of cylin-drical bar and tube are analyzed. By comparing the cylindrical tube whose ratio of outside diameter to internal diameter is 0.7 with the ...Based on the mechanics of material,the bending stiffness and intensity of cylin-drical bar and tube are analyzed. By comparing the cylindrical tube whose ratio of outside diameter to internal diameter is 0.7 with the cylindrical bar,it is concluded that when both of them have the same mass,the section stiffness of the cylindrical tube is three times that of the cylindrical bar;when both of them have the same external diameter,the mass of the cylindrical tube is only 1/2 that of the cylindrical bar,but the section stiffness of the cylindrical tube is 3/4 that of the cylindrical bar. By virtue of the elemental elastic-plastic theory,the yield stress of the liquid-filled cylindrical tube is investigated. Due to the incompressibility of liquid and the strain hardening effect of material,the yield stress of the liquid-filled tube is enlarged compared with the hollow tube,thus raising its bending intensity. Under the dy-namic load,compared with the hollow tube,the impact resistance of the liquid-filled tube is also raised due to elastic recovery. Because the hydraulic pressures per-pendicular to the inner surface are identical everywhere,the local stress concen-tration resulting from the ovalisation of the tube would be decreased,and the re-sistance to buckling would be improved.展开更多
In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore m...In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle bonding.Sound absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam layers.For graded foam of two distinct pore sizes,a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves,thereby aiding in graded foam design.An increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound source.The sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is increased.The sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound source.Given the same composition of foam with a fixed thickness proportion of pore sizes,one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical applications.This study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.展开更多
基金Supported by:Joint Research Fund for Earthquake Science,launched by the National Natural Science Foundation of China and the China Earthquake Administration under Grant No.U2039208。
文摘A diagonal or lumped mass matrix is of great value for time-domain analysis of structural dynamic and wave propagation problems,as the computational efforts can be greatly reduced in the process of mass matrix inversion.In this study,the nodal quadrature method is employed to construct a lumped mass matrix for the Chebyshev spectral element method(CSEM).A Gauss-Lobatto type quadrature,based on Gauss-Lobatto-Chebyshev points with a weighting function of unity,is thus derived.With the aid of this quadrature,the CSEM can take advantage of explicit time-marching schemes and provide an efficient new tool for solving structural dynamic problems.Several types of lumped mass Chebyshev spectral elements are designed,including rod,beam and plate elements.The performance of the developed method is examined via some numerical examples of natural vibration and elastic wave propagation,accompanied by their comparison to that of traditional consistent-mass CSEM or the classical finite element method(FEM).Numerical results indicate that the proposed method displays comparable accuracy as its consistent-mass counterpart,and is more accurate than classical FEM.For the simulation of elastic wave propagation in structures induced by high-frequency loading,this method achieves satisfactory performance in accuracy and efficiency.
文摘From the Boltzmann's constitutive law of viscoelastic materials and the linear theory of elastic materials with voids, a constitutive model of generalized force fields for viscoelastic solids with voids was given. By using the variational integral method, the convolution-type functional was given and the corresponding generalized variational principles and potential energy principle of viscoelastic solids with voids were presented. It can be shown that the variational principles correspond to the differential equations and the initial and boundary conditions of viscoelastic body with voids. As an application, a generalized variational principle of viscoelastic Timoshenko beams with damage was obtained which corresponds to the differential equations of generalized motion and the initial and boundary conditions of beams. The variational principles provide a way for solving problems of viscoelastic solids with voids.
基金Natural Sciences and Engineering Research Council of Canada for the financial support through its ICP and CRD programs(IRCPJ 461745-12 and RDCPJ 445200-12)as well as the industrial partners of the NSERC industrial chair on eco-responsible wood construction(CIRCERB)
文摘Decorative wood panels containing pouches of bio-based phase changing materials(PCMs) were prepared. Three different PCM mixtures were used: a blend of capric and lauric acids as well as two commercial products, Puretemp?20 and Puretemp?23(Puretemp). The panels consist of engraved Medium Density Fiberboard(MDF) filled with a plastic pouch filled with PCM. High density fiberboard(HDF) was used on top of the panels to enclose the PCM pouches. PCM mixtures were first tested by differential scanning calorimetry(DSC). Phase change temperature and total heat storage of the panels were measured for both fusion and solidification with a Dynamic Heat-Flow Meter Apparatus(DHFMA). DSC and DHFMA results were compared, allowing a better understanding of results gathered from these two techniques. DSC calibration has been revealed important when assessing PCMs. The panels present a phase change temperature and a latent heat storage suitable for buildings applications. The panel made with Puretemp?23 presented the highest energy, with 57.1 J g^(-1). Thermal cycling was conducted on the panels to investigate thermal reliability, which revealed small modifications of thermal properties for two products. For all cases, latent heat was found stable. Hygro-mechanical behavior of the panels was also evaluated as these where designed to be esthetic decorative panels. This study exposes the potential of a new type of wood-based panels loaded with PCM for thermal energy storage and brings overall knowledge about PCM products thermal characterization.
文摘Product system design is a mature concept in western developed countries. It has been applied in war industry during the last century. However,up until now,functional combination is still the main method for product system de-sign in China. Therefore,in terms of a concept of product generation and product interaction we are in a weak position compared with the requirements of global markets. Today,the idea of serial product design has attracted much attention in the design field and the definition of product generation as well as its parameters has already become the standard in serial product designs. Although the design of a large-scale NC machine tool is complicated,it can be further optimized by the precise exercise of object design by placing the concept of platform establishment firmly into serial product de-sign. The essence of a serial product design has been demonstrated by the design process of a large-scale NC machine tool.
基金the partial support of the Joint Research Fund for Earthquake Science launched by the National Natural Science Foundation of China and China Earthquake Administration(Grant No.U2039208)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX22_1322).
文摘In this article,several spectral models describing the stationary stochastic process of earthquake ground motion are explored and compared.The Hu-Zhou spectrum,which is regarded as an improved model of the Kanai-Tajimi spectrum,is concerned.It is proven that the earthquake-induced ground acceleration process described by the Hu-Zhou spectrum is a twice filtered white noise process in essence,and two filters for modifying low-frequency components and moderate-and high-frequency components respectively are investigated.A total of 1946 strong earthquake records at different sites were employed to determine the parameters of spectral models,including the Kanai-Tajimi spectrum,the Clough-Penzien spectrum and the Hu-Zhou spectrum.The results showed that the Hu-Zhou spectrum fits well with the actual observed ground motions over the whole frequency range,and that it is not only distinct in physical meaning and concise in mathematical expression,but also reasonable in practice.
基金The National Natural Science Foundation of China,Grant/Award Numbers:21972038,11921002,12202248National Key R&D and Transformative Technology Key Special Projects,Grant/Award Number:2021YFA0716703-2+4 种基金China Agriculture Research System of MOF and MARA,Grant/Award Number:CARS-04-PS-28Henan Province High-level Talent International Training Project,Grant/Award Number:Yuke(2020)145Top-Notch Talent Program of Henan Agricultural University,Grant/Award Number:30501307China Postdoctoral Science Foundation,Grant/Award Number:2021M701905Science and Technology Project of Henan Province,Grant/Award Number:232102111020。
文摘Control of the directional bounce of droplets impacting solid surfaces is crucial for many agricultural and industrial applications.However,for the universal impact process of raindrops on plant leaves,little is known about how the highly coupled and complicated fluid–structure interaction controls the postimpact motion of droplets and endows the leaves with tenacious vitality.Here,we report a leaf-like superhydrophobic cantilever to flexibly bounce droplets with well-defined directionality and controllability.Through theoretical modeling and three-dimensional fluid–solid coupling simulations,we find that the flexible cantilever significantly relieves the impacting forces of raindrops to reduce droplet fragmentation and enhance water repellency.The results further uncover the scaling relations of the droplet bouncing direction with respect to Weber number and cantilever stiffness.By this technique,the seemed disorganized postimpact movements of droplets are programmable and predictable,achieving the goal of where to point and where to hit automatically.This work advances the understanding of natural droplet impact phenomena,opens a new avenue for delicately controlling liquid motion in space with soft materials,and inspires a plethora of applications like soft robots to transport materials and energies,monitor plant growth as well as predict pathogen transmission in plants.
基金Supported by the Innovation Foundation of Jilin University and "985 Project" of Jilin University
文摘Based on the mechanics of material,the bending stiffness and intensity of cylin-drical bar and tube are analyzed. By comparing the cylindrical tube whose ratio of outside diameter to internal diameter is 0.7 with the cylindrical bar,it is concluded that when both of them have the same mass,the section stiffness of the cylindrical tube is three times that of the cylindrical bar;when both of them have the same external diameter,the mass of the cylindrical tube is only 1/2 that of the cylindrical bar,but the section stiffness of the cylindrical tube is 3/4 that of the cylindrical bar. By virtue of the elemental elastic-plastic theory,the yield stress of the liquid-filled cylindrical tube is investigated. Due to the incompressibility of liquid and the strain hardening effect of material,the yield stress of the liquid-filled tube is enlarged compared with the hollow tube,thus raising its bending intensity. Under the dy-namic load,compared with the hollow tube,the impact resistance of the liquid-filled tube is also raised due to elastic recovery. Because the hydraulic pressures per-pendicular to the inner surface are identical everywhere,the local stress concen-tration resulting from the ovalisation of the tube would be decreased,and the re-sistance to buckling would be improved.
基金supported by A*STAR under the AME YIRG Grant(No.A20E6c0099)AME IAF-PP Grant(No.A1896a0034)。
文摘In this study,functionally graded foam made of Inconel 625 superalloy was successfully produced using the template replication method,with open-cell polyurethane foams as a precursor.The products have a similar pore morphology as the templates and adjacent layers were successfully sintered together by particle bonding.Sound absorption experiments on graded metallic foams reveal that the sound absorption at particular frequency ranges can be improved by various permutations of foam layers.For graded foam of two distinct pore sizes,a mathematical equation was proposed to predict the location of the intersection point of the sound absorption curves,thereby aiding in graded foam design.An increase in sound absorption coefficients by resonance-like effects can be introduced before the intersection points by placing the foam layer of smaller pore size nearer to the sound source.The sound absorption performances can be further customized when the thickness proportion of the pore sizes is changed and when the number of distinct pore sizes used is increased.The sound absorption performance at lower frequencies is generally boosted by resonance-like effects when the layer of foam with the largest pore size is placed furthest from the sound source.Given the same composition of foam with a fixed thickness proportion of pore sizes,one can introduce resonance-like effects to improve the sound absorption performance compared to other permutations while possibly satisfying weight requirements in practical applications.This study provides valuable insights and mathematical guidelines in the design and manufacturing of functionally graded metallic foam for specific applications.
