This paper is devoted to the linear analysis of a slender homogeneous piezoelectric beam that undergoes tip loading. The solution of the Saint-Venant’s problem presented in this paper generalizes the known solution for a homogeneous elastic beam. The analytical approach in this study is based on the Saint-Venant’s semi-inverse method generalized to electroelasticity, where the stress, strain, and (electrical) displacement components are presented as a set of initially assumed expressions that contain tip parameters, six unknown coefficients, and three pairs of auxiliary (torsion/bending) functions in two variables. These pairs of functions satisfy the so-called coupled Neumann problem (CNP) in the cross-sectional domain. In the limit “elastic” case the CNP transforms to the Neumann problem, for a beam made of a poled piezoceramics the CNP is decomposed into two Neumann problems. The paper develops concepts of the torsion/bending functions, the torsional rigidity and shear center, the tip coupling matrix for a piezoelectric beam. Examples of exact and numerical solutions for elliptical and rectangular beams are presented.

A pseudo-Riemannian manifold endowed with k > 2 orthogonal complementary distributions (called a Riemannian almost multi-product structure) appears in such topics as multiply warped products, the webs composed of several foliations, Dupin hypersurfaces and in studies of the curvature and Einstein equations. In this article, we consider the following two problems on the mixed scalar curvature of a Riemannian almost multi-product manifold with a linear connection: a) integral formulas and applications to splitting of manifolds, b) variation formulas and applications to the mixed Einstein-Hilbert action, and we generalize certain results on the mixed scalar curvature of pseudo-Riemannian almost product manifolds.

We examine the total mixed scalar curvature of a smooth manifold endowed with a distribution as a functional of a pseudo-Riemannian metric. We develop variational formulas for quantities of extrinsic geometry of the distribution and use this key and technical result to find the critical points of this action. Together with the arbitrary variations of the metric, we consider also variations that preserve the volume of the manifold or partially preserve the metric (e.g., on the distribution). For each of those cases, we obtain the Euler-Lagrange equation and its several solutions. Examples of critical metrics that we find are related to various fields of geometry such as contact and 3-Sasakian manifolds, geodesic Riemannian flows, codimension-one foliations, and distributions of interesting geometric properties (e.g., totally umbilical and minimal).

We develop variation formulas on almost-product (e.g. foliated) pseudo-Riemannian manifolds, and we consider variations of metric preserving orthogonality of the distributions. These formulae are applied to Einstein-Hilbert type actions: the total mixed scalar curvature and the total extrinsic scalar curvature of a distribution. The obtained Euler-Lagrange equations admit a number of solutions, e.g., twisted products, conformal submersions and isoparametric foliations. The paper generalizes recent results about the actions on codimension-one foliations for the case of arbitrary (co)dimension.