Canonical Foliations of Certain Classes of Almost Contact Metric Structures

The purpose of this paper is to study the canonical foliations of an almost cosymplecticor almost Kenmotsu manifold M in a unified way.We prove that the canonical foliation definedby the contact distribution is Riemannian and tangentially almost K hler of codimension 1 and that is tangentially K hler if the manifold M is normal.Furthermore,we show that a semi-invariantsubmanifotd N of such a manifold M admits a canonical foliationwhich is defined by the anti-invariant distribution and a canonical cohomology class c(N) generated by a transversal volume formfor.In addition,we investigate the conditions when the even-dimensional cohomology classes ofN are non-trivial.Finally,we compute the Godbillon-Vey class for.