“…This is also motivated by the fact that a large variety of problems in Mathematical Fluid Mechanics are studied in unbounded pipes or in a system of unbounded pipes (that is, domains having non-compact boundaries); see in particular the celebrated Leray problem [64], the works of Ladyzhenskaya & Solonnikov [48,51], Amick [4,5], Pileckas et al [37,69] and the recent articles [76,77]. Nevertheless, not only the numerical approximation of these problems must be set in bounded domains (finite pipes or conjunction of finite pipes) [35], also theoretical approaches have been devised in regions with compact boundaries (for example, Leray's argument on the invading domains [45,55]) in order to tackle the original problem, thereby introducing artificial boundary conditions on truncating surfaces, see the articles by Blazy, Nazarov & Specovius-Neugebauer [9,59] and references therein. A second natural question then arises:…”