Topological Charge and Asymptotic Phase Invariants of Vortex Laser Beams

It is well known that the orbital angular momentum (OAM) of a light field is conserved on propagation. In this work, in contrast to the OAM, we analytically study conservation of the topological charge (TC), which is often confused with OAM, but has quite different physical meaning. To this end, we propose a huge-ring approximation of the Huygens–Fresnel principle, when the observation point is located on an infinite-radius ring. Based on this approximation, our proof of TC conservation reveals that there exist other quantities that are also propagation-invariant, and the number of these invariants is theoretically infinite. Numerical simulation confirms the conservation of two such invariants for two light fields. The results of this work can find applications in optical data transmission to identify optical signals.

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

When submitted to high external pressure, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.

A Comparative Buckling Study for the Carcass Layer of Flexible Pipes

When there are some failures on the external plastic layer of a flexible pipe, a high value of hydrostatic pressure can be transferred to its interlocked carcass layer, maybe causing a collapse. So it is necessary to predict on the design of a flexible pipe the maximum value of pressure that would be acceptable to avoid collapse of the carcass layer. That value depends on the imperfections on the internal diameter due to fabrication uncertainties. To study that problem, two numerical finite element models were created and used to simulate external pressure loading condition. The first model is a full 3D approximation, composed by solid elements. The second one is a 3D ring approximation, still made by solids. An analytical model using an equivalent thickness approach for carcass was done. A good correlation between analytical and numerical models was achieved for pre-buckling behavior, but analytical buckling behavior was not the same as numerical values predictions. Discussions about these differences are done.