A metamaterial vibration isolator,termed as wave-insulating isolator,is proposed,which preserves enough load-bearing capability and offers ultra-low and broad bandgaps for greatly enhanced wave insulation.It consists ...A metamaterial vibration isolator,termed as wave-insulating isolator,is proposed,which preserves enough load-bearing capability and offers ultra-low and broad bandgaps for greatly enhanced wave insulation.It consists of plate-shaped metacells,whose symmetric and antisymmetric local resonant modes offer several low and broad mode bandgaps although the complete bandgap remains high and narrow.The bandgap mechanisms,vibration isolation properties,effects of key parameters,and robustness to complex conditions are clarified.As experimentally demonstrated,the wave-insulating isolator can improve the vibration insulation in the ranges of[50 Hz,180 Hz]and[260 Hz,400 Hz]by 15 dB and 25 dB,respectively,in contrast to the conventional isolator with the same first resonant frequency.展开更多
Combining periodic layered structure with three-dimensional cylindrical local resonators,a hybrid metastructure with improved wave isolation ability was designed and investigated through theoretical and numerical appr...Combining periodic layered structure with three-dimensional cylindrical local resonators,a hybrid metastructure with improved wave isolation ability was designed and investigated through theoretical and numerical approaches.The metastructure is composed of periodic rubber layers and concrete layers embedded with three-dimensional resonators,which can be freely designed with multi local resonant frequencies to attenuate vibrations at required frequencies and widen the attenuation bandgap.The metastructure can also effectively attenuate seismic responses.Compared with layered rubber-based structures,the metastructure has more excellent wave attenuation effects with greater attenuation and wider bandgap.展开更多
The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves.In this paper,a metastructure(MS)composed of floating periodic pontoons is proposed for broadband wate...The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves.In this paper,a metastructure(MS)composed of floating periodic pontoons is proposed for broadband water wave attenuation.The interaction of surface gravity waves with the MS is investigated using linear wave theory.The potential solutions of water waves by the MS with a finite array are developed by using the eigenfunction expansion matching method(EEMM),and the band structure of the MS is calculated by the transfer matrix method(TMM),in which the evanescent modes of waves are considered.The solution is verified against the existing numerical result for a special case.Based on the present solution,the association between Bragg resonance reflection and Bloch bandgaps is examined,the effects of pontoon geometry are analyzed,and the comparison between floating MS and bottom-mounted periodic structures is conducted.A computational fluid dynamics(CFD)model is further developed to assess the structures in practical fluid environments,and the floating MS presents excellent wave attenuation performance.The study presented here may provide a promising solution for protecting the coast and offshore structures.展开更多
Traditional vibration isolation structures cannot work effectively for low-frequency vibration under heavy loads,due to the inherent contradiction between the high-static and lowdynamic stiffness of these structures.A...Traditional vibration isolation structures cannot work effectively for low-frequency vibration under heavy loads,due to the inherent contradiction between the high-static and lowdynamic stiffness of these structures.Although the challenge can be effectively addressed by introducing a negative stiffness mechanism,the existing structures inevitably have complex configurations.Metastructures,a class of man-made structures with both extraordinary mechanical properties and simple configurations,provide a new insight for low-frequency vibration isolation technology.In this paper,circular metastructure isolators consisting of some simple beams are designed for low-frequency vibration,including a single-layer isolator and a double-layer isolator,and their static and dynamic characteristics are studied,respectively.For the static characteristic,the force–displacement and stiffness–displacement curves are obtained by finite element simulation;for the dynamic characteristic,the vibration transmissibility curves are obtained analytically and numerically.The result shows that the circular nonlinear single-layer isolator has excellent lowfrequency isolation performance,and the isolation frequency band will decrease about 20 Hz when the isolated mass is fixed at 1.535 kg,compared with a similar circular linear isolator.These static and dynamic properties are well verified through experiments.Our work provides an innovative approach for the low-frequency vibration isolation and has wide potential applications in aeronautics.展开更多
Sic-based composites are widely used as electromagnetic wave absorbers due to their excellent dielectric properties.However,the constraints associated with structural design and the intricacies of the preparation proc...Sic-based composites are widely used as electromagnetic wave absorbers due to their excellent dielectric properties.However,the constraints associated with structural design and the intricacies of the preparation process hinder their broader application.In this study,novel mullite anti-gyroid/SiC gyroid metastructures are designed to integrate the mechanical and electromagnetic wave(EMW)absorption properties of composite materials.Mullite anti-gyroid/SiC gyroid composites are fabricated utilizing a combination of digital light processing(DLP)three-dimensional(3D)printing and precursor infiltration and pyrolysis(PiP)processes.Through the modulation of structural units,the electromagnetic parameters can be effectively regulated,thus improving the impedance matching characteristics of the composites.The structural composites show outstanding EMW absorption properties,with a minimum reflection loss of-54 dB at a thickness of 1.9 mm and an effective absorption bandwidth of 3.20 GHz at a thickness of 2.2 mm.Furthermore,the PIP process significantly enhances the mechanical properties of the composites;compared with those of the mullite/SiC ceramics,the flexural strength of the composites is improved by 3.69-5.85 times(13.28±1.15 MPa vs.(49.05±1.07)-(77.78±3.72)MPa),and the compressive strength is improved by 4.59-13.58 times(8.55±0.90 MPa vs.(39.02±1.63)-(116.13±2.58)MPa).This approach offers a novel and effective method for fabricating structural composites with an expanded range of higher electromagnetic wave absorption properties and improved mechanical properties.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52241103 and 52322505)the Natural Science Fund for Distinguished Young Scholars of Hunan Province of China(No.2023JJ10055)。
文摘A metamaterial vibration isolator,termed as wave-insulating isolator,is proposed,which preserves enough load-bearing capability and offers ultra-low and broad bandgaps for greatly enhanced wave insulation.It consists of plate-shaped metacells,whose symmetric and antisymmetric local resonant modes offer several low and broad mode bandgaps although the complete bandgap remains high and narrow.The bandgap mechanisms,vibration isolation properties,effects of key parameters,and robustness to complex conditions are clarified.As experimentally demonstrated,the wave-insulating isolator can improve the vibration insulation in the ranges of[50 Hz,180 Hz]and[260 Hz,400 Hz]by 15 dB and 25 dB,respectively,in contrast to the conventional isolator with the same first resonant frequency.
基金Supports from National Natural Science Foundation of China(Grant Nos.U20A20286 and 11972184)the Systematic Project of Guangxi Key Laboratory of Disaster Prevention and Engineering Safety(Grant No.2021ZDK006)+1 种基金Natural Science Foundation of Jiangsu Province of China(Grant No.BK20201286)Science and Technology Project of Jiangsu Province of China(Grant No.BE2020716)are gratefully acknowledged.
文摘Combining periodic layered structure with three-dimensional cylindrical local resonators,a hybrid metastructure with improved wave isolation ability was designed and investigated through theoretical and numerical approaches.The metastructure is composed of periodic rubber layers and concrete layers embedded with three-dimensional resonators,which can be freely designed with multi local resonant frequencies to attenuate vibrations at required frequencies and widen the attenuation bandgap.The metastructure can also effectively attenuate seismic responses.Compared with layered rubber-based structures,the metastructure has more excellent wave attenuation effects with greater attenuation and wider bandgap.
基金Project supported by the National Natural Science Foundation of China(No.12272128)the Natural Science Foundation of Jiangsu Province of China(No.BK20243019)。
文摘The narrow attenuation bands of traditional marine structures have long been a challenge in mitigating water waves.In this paper,a metastructure(MS)composed of floating periodic pontoons is proposed for broadband water wave attenuation.The interaction of surface gravity waves with the MS is investigated using linear wave theory.The potential solutions of water waves by the MS with a finite array are developed by using the eigenfunction expansion matching method(EEMM),and the band structure of the MS is calculated by the transfer matrix method(TMM),in which the evanescent modes of waves are considered.The solution is verified against the existing numerical result for a special case.Based on the present solution,the association between Bragg resonance reflection and Bloch bandgaps is examined,the effects of pontoon geometry are analyzed,and the comparison between floating MS and bottom-mounted periodic structures is conducted.A computational fluid dynamics(CFD)model is further developed to assess the structures in practical fluid environments,and the floating MS presents excellent wave attenuation performance.The study presented here may provide a promising solution for protecting the coast and offshore structures.
基金Supported by Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2024001)National Natural Science Foundation of China(Nos.11972296,12372157)+1 种基金Aeronautical Science Foundation of China(No.20220057053001)Open Project of State Key Laboratory for Strength and Vibration of Mechanical Structures of Xi’an Jiaotong University,China(No.SV2023-KF-19).
文摘Traditional vibration isolation structures cannot work effectively for low-frequency vibration under heavy loads,due to the inherent contradiction between the high-static and lowdynamic stiffness of these structures.Although the challenge can be effectively addressed by introducing a negative stiffness mechanism,the existing structures inevitably have complex configurations.Metastructures,a class of man-made structures with both extraordinary mechanical properties and simple configurations,provide a new insight for low-frequency vibration isolation technology.In this paper,circular metastructure isolators consisting of some simple beams are designed for low-frequency vibration,including a single-layer isolator and a double-layer isolator,and their static and dynamic characteristics are studied,respectively.For the static characteristic,the force–displacement and stiffness–displacement curves are obtained by finite element simulation;for the dynamic characteristic,the vibration transmissibility curves are obtained analytically and numerically.The result shows that the circular nonlinear single-layer isolator has excellent lowfrequency isolation performance,and the isolation frequency band will decrease about 20 Hz when the isolated mass is fixed at 1.535 kg,compared with a similar circular linear isolator.These static and dynamic properties are well verified through experiments.Our work provides an innovative approach for the low-frequency vibration isolation and has wide potential applications in aeronautics.
基金The authors gratefully acknowledged the financial support provided by the National Key R&D Program of China(No.2021YFB3701500)the Program of Shanghai Academic/Technology Research Leader(No.22XD1404000).
文摘Sic-based composites are widely used as electromagnetic wave absorbers due to their excellent dielectric properties.However,the constraints associated with structural design and the intricacies of the preparation process hinder their broader application.In this study,novel mullite anti-gyroid/SiC gyroid metastructures are designed to integrate the mechanical and electromagnetic wave(EMW)absorption properties of composite materials.Mullite anti-gyroid/SiC gyroid composites are fabricated utilizing a combination of digital light processing(DLP)three-dimensional(3D)printing and precursor infiltration and pyrolysis(PiP)processes.Through the modulation of structural units,the electromagnetic parameters can be effectively regulated,thus improving the impedance matching characteristics of the composites.The structural composites show outstanding EMW absorption properties,with a minimum reflection loss of-54 dB at a thickness of 1.9 mm and an effective absorption bandwidth of 3.20 GHz at a thickness of 2.2 mm.Furthermore,the PIP process significantly enhances the mechanical properties of the composites;compared with those of the mullite/SiC ceramics,the flexural strength of the composites is improved by 3.69-5.85 times(13.28±1.15 MPa vs.(49.05±1.07)-(77.78±3.72)MPa),and the compressive strength is improved by 4.59-13.58 times(8.55±0.90 MPa vs.(39.02±1.63)-(116.13±2.58)MPa).This approach offers a novel and effective method for fabricating structural composites with an expanded range of higher electromagnetic wave absorption properties and improved mechanical properties.
