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Ultrawide bandgap by 3D monolithic mechanical metastructure for vibration and noise control

Muhammad, Lim C. W.

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

197--207

EN

The all-direction vibration and noise control by metastructures have received high demands in the vibroacoustic community in the recent past to solve multiple vibration and noise-related engineering problems. This class of elastic metamaterial has grasped a strong root in this community due to its versatile wave manipulation characteristics, including frequency bandgap property. Inspired by the idea of metamaterial and computational mechanics in breakthrough research for vibration and noise control technology, the present study proposes a novel 3D phononic metastructure that is capable of generating low-frequency extremely wide three-dimensional complete bandgap with relative bandwidth Δω/ωc=171.5%. The study is based on analytical modeling, numerical finite element analysis and experiment on 3D printed prototype. The proposed monolithic metastructure is comprised of elastic beams connected orthogonally with rigid spherical masses. The axial compression mode of a complete unit cell structure and the flexural stiffness of beams are manipulated to generate low-frequency extremely wide bandgap. By the principle of modal masses participation/mode separation, the opening and closing of the bandgap is analyzed. The results are corroborated by two different numerical FE solutions on the frequency response spectrum, and the models are validated by performing a vibration test on 3D printed prototype. The wave attenuation over ultrawide frequency range is demonstrated through numerical and experimental approaches, and excellent agreement is reported. The proposed monolithic metastructure design may find potential applications in industrial and infrastructural devices where noise and vibration control over ultrawide frequency range are desirable in all directions.

2

Combined load buckling for cylindrical shells based on a symplectic elasticity approach

Sun J., Xu X., Lim C. W.

Journal of Theoretical and Applied Mechanics

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2016

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Vol. 54 nr 3

705--716

EN

Buckling behavior of cylindrical shells subjected to combined pressure, torsion and axial compression is presented by employing a symplectic method. Both symmetric and non- -symmetric boundary conditions are considered. Hamiltonian canonical equations are established by introducing four pairs of dual variables. Then, solution of fundamental equations is converted into a symplectic eigenvalue problem. It is concluded that the influence of pressure on buckling solutions is more significant than that due to compressive load, in particular for a longer external pressured cylindrical shell. Besides, buckling loads and circumferential wavenumbers can be reduced greatly by relaxed in-plane axial constraints.

3

Buckling of cylindrical shells under external pressure in a Hamiltonian system

Sun J., Xu X., Lim C. W.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 3

641--653

EN

In this article, the elastic buckling behavior of cylindrical shells under external pressure is studied by using a symplectic method. Based on Donnell’s shell theory, the governing equations which are expressed in stress function and radial displacement are re-arranged into the Hamiltonian canonical equations. The critical loads and buckling modes are reduced to solving for symplectic eigenvalues and eigenvectors. The buckling solutions are mainly grouped into four categories according to the natures of the buckling modes. The effects of geometrical parameters and boundary conditions on the buckling loads and modes are examined in detail.