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Transmission eigenvalues are of major interests in the inverse scattering theory for uniqueness. For the Helmholtz equation of isotropic inhomogeneous media with voids, the existence of transmission eigenvalues was studied for the Helmholtz equation under the refractive index perturbation of the media. Firstly, through construction of the Neumann-Dirichlet operator, the equivalent form of the transmission eigenvalue problem was obtained. Then, the eigenvalue function was built to transform the perturbation problem for transmission eigenvalues into the perturbation problem for zero eigenvalues of operators. Finally, the perturbation method based on the implicit function theorem was used to prove the existence of transmission eigenvalues. [ABSTRACT FROM AUTHOR]

For low-frequency noise control problems, a Helmholtz-type phononic crystal with an adjustable chamber was constructed. The inner chamber of the structure is divided into upper and lower chambers by a diaphragm connected by a movable telescopic screw. Meanwhile, an arch-shaped opening channel is adopted. Characteristics of bandgap and sound insulation of the structure are analyzed by finite element method, and equivalent models of the structure at the starting frequency and cut-off frequency of the bandgap are constructed by "acoustic-force analogy" method. The results show that the designed structure can generate six complete bandgaps within 500 Hz, and the lowest bandgap frequency can reach 31. 34 Hz. At the same time, it shows good sound insulation performance in each bandgap frequency band, and the maximum sound insulation is up to 111. 95 dB. Finally, by adjusting the telescopic screw and changing the cavity structure layout, multiple resonant bandgaps can be connected to form a wide bandgap, and achieve the purpose of adjusting the sound insulation band. This design provides a new idea for the sound insulation performance of Helmholtz type phononic crystals. [ABSTRACT FROM AUTHOR]

The PDE sensitivity filter can eliminate the checkerboard patterns and numerical instability existing in the topology optimization results of continuum structures, and the essence of the PDE sensitivity filter is the Helmholtz partial differential equation with Neumann boundary conditions. To solve the large-scale PDE sensitivity filter problem, the conjugate gradient algorithm, the multigrid algorithm and the multigrid preconditioned conjugate gradient algorithm were used to solve the algebraic equations obtained by finite element analysis, and the effects of accuracy, filter radius and grid numbers on the efficiency of topology optimization were studied. The results show that, compared with the conjugate gradient algorithm and the multi-grid algorithm, the multi-grid preconditioned conjugate gradient algorithm has the least number of iterations and the shortest running time, which greatly improves the efficiency of topology optimization. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Journal of Jilin University (Science Edition) / Jilin Daxue Xuebao (Lixue Ban) is the property of Zhongguo Xue shu qi Kan (Guang Pan Ban) Dian zi Za zhi She and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The problem of impedance boundary condition obstacle buried in different dielectric cylinders was discussed. By using the jump relationship and combined single and double-layer potentials theory, this problem was turned into boundary integral equations, then it transformed into solving linear system of equations by applying the Nyström method. Finally, for different scattering obstacles, the numerical examples were given to test the validity of the method. [ABSTRACT FROM AUTHOR]

The non linear equations governing wind-induced internal pressure responses for a two- compartment building with a windward dominant opening are derived based on some reasonable assumptions. The law of mass conservation, adiabatic equation, and the unsteady form of the Bernoulli equation are used for the derivation. Then, the improved method for the existing research result based on corresponding linear model is given. The numerical calculation results show that the effects of Helmhohz resonance on internal pressure responses have been neglected in the existing linear model, but it can be made up by the improved method proposed in this paper. [ABSTRACT FROM AUTHOR]

Based on Helmholtz boundary integral equation for calculating underwater radiation of cylindrical shell, a prediction method of acoustic radiation presented by means of surface vibration velocity grouping measurement accomplished by the vibration accelerometers that installed on the shell surface. A complicated multi-compartmental shell structure is designed and the underwater vibration-acoustic radiation experiments with single and multiple excitations are implemented. It shows that the prediction method is accurate and feasible through comparison between the calculating results and the experimental one. Finally the principle of vibration velocity grouping is discussed. [ABSTRACT FROM AUTHOR]

Because of amazing advantages of meshless numerical methods over classical finite difference methods and finite element methods, the point allocation method and its characteristics are introduced. Several techniques for derivative boundary conditions by meshless allocation method are summarized and a new technique based on integral interpolation is proposed. Using meshless allocation method based on point interpolation to solve Helmholtz problem, the superiority of the proposed technique is verified. [ABSTRACT FROM AUTHOR]

A meshless method for Helmholtz equations by collation with radial basis functions was structured, and the existence of only solution was given. The numerical solution of the Helmholtz equations was obtained by the new meshless method provided in this paper. Functions were obtained. The meshless method in this paper com- pared with the finite element method ,the other method of collation with radial basis functions, it will be more accurate and more valid. [ABSTRACT FROM AUTHOR]

The scattering problem for Helmholtz equation of partially coater obstacles where the scattered field satisfies mixed Neumann-impedance boundary condition was considered. In order to get the numerical method, single and double-layer potential are combined to change the mixed boundary problem to the integral equation. Numerical examples are given to show that this method is both accurate and easy to use. [ABSTRACT FROM AUTHOR]