טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMar-Or Assaf
SubjectComputational Schemes for Incorporating Global Information
in Limited-Area Models
DepartmentDepartment of Applied Mathematics
Supervisor Professor Dan Givoli


Abstract

The problem of global-regional model interaction (sometimes referred to in the literature as ``model nesting'' or ``grid nesting''), in which global information is incorporated into the regional model, is considered and the concept of one-way and two-way nesting is presented.


Following the introduction, Carpenter's lateral boundary condition, which is used for a one-way nesting scheme, and its relation to Sommerfeld's absorbing boundary condition is presented and analyzed in the context of the scalar one-dimensional wave problem. Carpenter's boundary scheme is then implemented and its performance is compared with other possible lateral boundary conditions and is shown to yield better results, as predicted by analysis of the continuous problem.


In the next part, the extension of Carpenter's lateral boundary scheme to two-dimensional problems is considered. For that purpose, the Hagstrom-Warburton family of high-order absorbing boundary conditions for the non-dispersive scalar wave-equation is presented, analyzed and then extended to dispersive and variable wave-speed media in the context of a two-dimensional wave-guide problem. Following a reformulation of the Hagstrom-Warburton absorbing boundary condition into operator form, it is then implemented in the extended Carpenter lateral boundary scheme for the two-dimensional wave problem. This ``Hagstrom-Warburton / Carpenter'' lateral boundary condition one-way nesting scheme is then investigated using a two-dimensional semi-infinite wave-guide model, and its performance is compared with that of Carpenter's original lateral boundary scheme.