Analysis and Applications

This work deals with the variation of the solution to an obstacle problem with respect to the variation of its parameters. More precisely, a mechanical structure is pushed by some external forces against an obstacle in such a way that the equilibrium solution involves a part of the domain in which the structure is strictly in contact with the obstacle. It is known from the theory of variational inequalities that studying the variation of the solution as the external forces vary amounts to studying the variation of the boundary of this contact zone. This problem has been studied in previous works in the scalar case, and it was open in the general case where the unknown is a vector field, due to the coupling between the components. As a first step, the present work considers the case of a linearly elastic shallow membrane shell where the coupling between the in-plane and normal components of the displacement arises from the curvature.

A time-periodic Stokes problem set in a domain with cylindrical outlets to infinity is studied. We derive the generalized Green formula. It enables us to impose so-called asymptotic conditions at infinity which allow to determine a unique time-periodic solution. This method was proposed and applied for a steady Stokes problem by Nazarov and co-authors.

In this paper, we establish local existence of solutions of a variant of a system derived by Choi and Camassa [Weakly nonlinear internal waves in a two-fluids system, J. Fluid Mech. 313 (1996) 83–103] to describe the propagation of an internal wave at the interface of two immiscible fluids with constant densities. We also present a numerical solver to approximate the solutions of the Cauchy problem.

We present a semi-local convergence analysis of Newton’s method in order to approximate a locally unique solution of a nonlinear equation in a Banach space setting. Using center-Lipschitz condition on the first and the second Fréchet derivatives, we provide under the same computational cost a new and more precise convergence analysis than in earlier studies by Huang [A note of Kantorovich theorem for Newton iteration, J. Comput. Appl. Math. 47 (1993) 211–217] and Gutiérrez [A new semilocal convergence theorem for Newton’s method, J. Comput. Appl. Math. 79 (1997) 131–145]. Numerical examples where the old convergence criteria cannot apply to solve nonlinear equations but the new convergence criteria are satisfied are also presented at the concluding section of this paper.

We prove some regularity criteria for the incompressible magnetohydrodynamic equations with partial viscosity. We study three cases: incompressible magnetohydrodynamic equations with zero viscosity in a bounded domain, incompressible magnetohydrodynamic equations with zero resistivity in a bounded domain, and the density-dependent magnetohydrodynamic equations with zero heat conductivity and zero resistivity in the whole space ${ℝ}^3$. Our results extend and improve some known results.