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Approximate solution of second kind integral equations on infinite cylindrical surfaces
The paper considers second kind integral equations of the form (abbreviated)φφK+=g, in which S is an infinite cylindrical surface of arbitrary smooth cross-section. The “truncated equation” (abbreviated )aaaaKEφφ+=g, obtained by replacing S by Sa, a closed bounded surface of class C2, the boundary of a section of the interior of S of length 2a, is also discussed. Conditions on k are obtained (in particular, implying that K commutes with the operation of translation in the direction of the cylinder axis) which ensure that I-K is invertible, that I - Ka is invertible and (I — Ka)-1 uniformly bounded for all sufficiently large a, and that aφ converges to φ in an appropriate sense as ∞→a. Uniform stability and convergence results for a piecewise constant boundary element collocation method for the truncated equations are also obtained.
A boundary integral equation, which models three-dimensional acoustic scattering from an infi- nite rigid cylinder, illustrates the application of the above results to prove existence of solution (of the integral equation and the corresponding boundary value problem) and convergence of a particular collocation method
Asymptotic behaviour at infinity of solutions of second kind integral equations on unbounded regions of Rn
We consider second kind integral equations of the form x(s) - (abbreviated x - K x = y ), in which Ω is some unbounded subset of Rn. Let Xp denote the weighted space of functions x continuous on Ω and satisfying x (s) = O(|s|-p ),s → ∞We show that if the kernel k(s,t) decays like |s — t|-q as |s — t| → ∞ for some sufficiently large q (and some other mild conditions on k are satisfied), then K ∈ B(XP) (the set of bounded linear operators on Xp), for 0 ≤ p ≤ q. If also (I - K)-1 ∈ B(X0) then (I - K)-1 ∈ B(XP) for 0 < p < q, and (I- K)-1∈ B(Xq) if further conditions on k hold. Thus, if k(s, t) = O(|s — t|-q). |s — t| → ∞, and y(s)=O(|s|-p), s → ∞, the asymptotic behaviour of the solution x may be estimated as x (s) = O(|s|-r), |s| → ∞, r := min(p, q). The case when k(s,t) = к(s — t), so that the equation is of Wiener-Hopf type, receives especial attention. Conditions, in terms of the symbol of I — K, for I — K to be invertible or Fredholm on Xp are established for certain cases (Ω a half-space or cone).
A boundary integral equation, which models three-dimensional acoustic propaga-tion above flat ground, absorbing apart from an infinite rigid strip, illustrates the practical application and sharpness of the above results. This integral equation mod-els, in particular, road traffic noise propagation along an infinite road surface sur-rounded by absorbing ground. We prove that the sound propagating along the rigid road surface eventually decays with distance at the same rate as sound propagating above the absorbing ground