JaLCDOI 10.18926/15512
FullText URL Mem_Fac_Eng_OU_25_2_69.pdf
Author Tsuchiya Takao| Kagawa, Yukio|
Abstract A finite element approach to the calculation of nonlinear sound propagation is proposed. Under the assumption of a weak nonlinearity, a linearized one-dimensional equation is considered. The equation is discretized in space, and is then solved for time by using Newmark-β integration scheme, in which a numerical damping is devised. Some numerical demonstrations are made for the nonlinear sound propagation of a single-shot pulse in air. It is shown that the shock wave propagation is stably and accurately simulated by the introduction of the numerical damping.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1991-03-28
Volume volume25
Issue issue2
Start Page 69
End Page 80
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307747
JaLCDOI 10.18926/15379
FullText URL Mem_Fac_Eng_OU_30_1_63.pdf
Author Koshimoto Marcos| Mahmood Zaheed| Kagawa, Yukio|
Abstract Optical fibers or integrated optical waveguides have arbitrary cross-sectional index or refraction distribution. An efficient finite element method for analyzing the propagation characteristics of dielectric / optical waveguides with open boundary is presented. The propagation modes are hybrid, for which a variational expression is formulated in terms of the longitudinal electric and magnetic field components. Infinite elements are introduced to consider open boundary or to extend the region to infinity. Several specific examples are given and the results are compared with those obtained by other approximate methods. Very close agreements have been found.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1995-12-28
Volume volume30
Issue issue1
Start Page 63
End Page 73
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307545
JaLCDOI 10.18926/15377
FullText URL Mem_Fac_Eng_OU_30_1_47.pdf
Author Kagawa, Yukio| Sun Yonghao| Mahmood Zaheed|
Abstract Regular boundary element method is employed for the variational formulation of Helmholtz equation that governs the waveguiding problems. Like in the Charge simulation method, in this method, the source points associated with the fundamental solutions are allocated outside the domain so that the singular integrals which occur in the standard boundary element procedure can be avoided. First, the formulation is developed for the two-dimensional scalar Helmholtz problem solving for the axial components of either electric or magnetic fields. The application of the formulation is shown for simple hollow rectangular waveguide and dielectric-slab-loaded rectangular waveguide. Then the formulation is extended for the analysis of dielectric waveguides of open type incorporating axial components of both electric and magnetic fields, for the solution of the propagating modes which are generally of hybrid types. To show the validity and quality of the formulation, it is applied to a circular step-index optical waveguide and a dielectric rectangular waveguide. Very close agreements have been found when the solutions are compared with the ones obtained by different methods. One distinct merit of the extended formulation is that it has been fixed to suppress the spurious solutions which are encountered while solved by the conventional boundary element method.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1995-12-28
Volume volume30
Issue issue1
Start Page 47
End Page 62
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307187
JaLCDOI 10.18926/15374
FullText URL Mem_Fac_Eng_OU_30_1_35.pdf
Author Mahmood Zaheed| Kagawa, Yukio|
Abstract Divergence-free shape functions are proposed for the finite elements, with which inhomogeneously-loaded and arbitrarily-shaped waveguides are analysed. The method is based on vectorial finite element formulation employing edge elements. The shape functions used for the approximation of the fields are shown analytically to be divergence-free and as an evidence, the non-physical solutions that appeared in the longitudinal component finite element formulation have been shown to be absent. To show the validity of the elements, application is made for the analysis of rectangular waveguides loaded with dielectric slab and a waveguide with curved structure. The solutions obtained are compared with the analytical ones or the solutions reported elsewhere. The degree of accuracy has been found satisfactory.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1995-12-28
Volume volume30
Issue issue1
Start Page 35
End Page 46
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307293
JaLCDOI 10.18926/15372
FullText URL Mem_Fac_Eng_OU_30_1_25.pdf
Author Sun Yonghao| Kagawa, Yukio|
Abstract Identification of unknown electric charges or sources distributed in space is made from the data observed over the field boundary using dual reciprocity boundary element models. The inhomogeneous term of the Poisson field can equivalently be expressed as the linear combination of the functions associated with the particular solutions to transform into Laplace equation. For the solution procedure, the variational formulation is employed, in which the regular boundary integral approach is incorporated to avoid the singularity. Numerical examples are presented to demonstrate the availability and the capability.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 1995-12-28
Volume volume30
Issue issue1
Start Page 25
End Page 33
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307314
JaLCDOI 10.18926/15357
FullText URL Mem_Fac_Eng_OU_35_53.pdf
Author Kim Tae Yong| Kagawa, Yukio|
Abstract Fresnel zone plate lens (FZPL) has widely been used in electromagnetic antenna applications. Most analysis method based on the potential (scalar) wave approximation has been applied to a few very limited and simplified cases. The present paper analyzes the FZPL in more general form including the diffraction and transmission using the method of moments (MoM). The focusing gain characteristics in the oblique incidence as well as in the normal incidence are considered. The MoM solution using the three-dimensional vectorial formulation requires a large memory space for the FZPL as it is operated at a short wavelength. This is simply overcome by using an iterative conjugate gradient method for the numerical evaluation. The MoM solutions are compared with the other solutions.
Publication Title Memoirs of the Faculty of Engineering, Okayama University
Published Date 2001-03-27
Volume volume35
Issue issue1-2
Start Page 53
End Page 61
ISSN 0475-0071
language 英語
File Version publisher
NAID 120002307849