Parametric Study of Steel-Lined pressure Shafts in Anisotropic Rock
Steel-lined pressure tunnels and shafts are used to convey water from the reservoir to the turbines in high-head hydroelectric power plants. An axisymmetrical multilayer model is of-ten considered by engineers for the design of the steel liner. Stresses and deformations can then be computed with a closed-form analytical solution in isotropic rock. When the rock is anisotropic, the lowest elastic modulus of the rock measured in situ is often considered in the analytical solu-tion, which is regarded as conservative. In this work, the behaviour of steel liners in anisotropic rock was studied systematically by means of the Finite Element Method (FEM). The materials, namely steel, backfill concrete, near-field rock and far-field rock were modelled as linear and elas-tic, and a tied contact was assumed between the layers. The influence of geometrical and material parameters under a quasi-static internal water pressure was studied through an extensive para-metric study. It was observed that, compared to the corresponding results in isotropic rock, maxi-mum stresses in the steel-liner can be reduced up to 25% when anisotropy is considered. On the contrary, the maximum stresses in the far-field rock can be largely underestimated, namely up to 65%.
A review of wave celerity in frictionless and axisymmetrical steel-lined pressure tunnels
Generally applicable approaches for estimating the‘‘quasi-static’’, which means without fluid–structure interaction and frequency-dependent water-hammer wave speed in steel-lined pressure tunnels are analyzed. The external constraints and assumptions of these approaches are discussed in detail. The reformulated formulas are then compared to commonly used expressions. Some special cases of wave speed calculation such as unlined pressure tunnels and open-air penstocks are investigated. The quasi-static wave speed is significantly influenced by the state of the back fill concrete and the near-field rock zone (crackedoruncracked). In the case when the set wo layers are cracked, the quasi-static wave speed is over estimated in between 1% and 8%compared to uncracked concrete and near field rocklayers. Depending on the stiff ness of steel liner and penstock, the fluid–structure interaction leads to significant difference in wave speeds values. Compared to the quasi-staticcase, the fluid–structure interaction approach, applied to steel-lined tunnels, results up to 13%higher wave speed values in the high-frequency range (higher than 600Hz)and up to 150% lower values for frequencies between 150 and 300 Hz in the considered test case.
Ultrastructural observations of the spermiogenesis in the Parotoplaninae (Plathelminthes, Proseriata) with special reference to a striated appendage of the intercentriolar body
SummaryThe spermiogenesis of three species of the Parotoplaninae (Otoplanidae, Proseriata) is described based on electron-microscopical observations. Special reference is given to organelles which do not persist in mature male gametes. One of these organelles is a striated appendage of the intercentriolar body. This differentiation has not been reported from any other plathelminth taxa up to now. The striated appendage, which may serve as a strengthening element, is hypothesized to be an autapomorphic feature of the Parotoplaninae.