Study on calculation method of stability for embedded penstocks with stiffener ring under external pressure

A three-dimensional FEM(finite element model)is established, including penstocks with initial defect (ovality), backfill concrete, drainage cushion and surrounding rock. The nonlinear static calculation of the model is carried out. The stability of penstocks with backfill concrete, drainage cushion and surrounding rock under external pressure is studied. The sensibility of the embedded penstocks to initial defect, initial gap and elastic modulus of drainage cushion is analyzed. The results of finite element method, Jacobsen method and strength formula in SL281 are compared and analyzed. The results indicate that the FEM of penstocks, backfill concrete and surrounding rock with initial defects is easy to converge by nonlinear calculation; the ovality and gap have little influence on the critical external pressure of the embedded penstocks with stiffener ring, while the drainage cushion has a certain influence on the critical external pressure; the critical external pressure calculated by SL281 is low and safe; compared with Jacobsen method, the critical external pressure of the finite element method is increased by about 14%; for the embedded penstocks with drainage cushion, the finite element method can be used to calculate the influence of the drainage cushion on the critical external pressure, and the appropriate reduction factor can be obtained, and then the Jacobsen result can be modified by the reduction factor.

Scale Dependent Critical External Pressure for Buckling of Spherical Shell Based on Nonlocal Strain Gradient Theory

Instabilities in nanosized, externally pressurized spherical shells are important for their applications in nano and biotechnology. Mechanics at such length scale is described by nonlocal and Strain Gradient (SG) field theories. However, analysis of shell buckling is involved and becomes even more complicated in presence of nonlocal and SG interactions. This paper demonstrates that such analysis can be largely simplified by a shallow segment representation of the shell by assuming short wave lengths for the incipient buckling modes. The governing equations are derived and linearized equations are solved to obtain a closed form solution for the critical external pressure causing buckling for a pressurized nonlocal shell. Nonlocal interactions are shown to reduce, whereas the SG interaction increases the critical pressure. The relative reduction/increase becomes more prominent for higher modes of buckling and for increasingly thinner shell. A constricting relationship between the two set of wave numbers expressing the buckling modes is also shown to be modified by the nonlocal and SG scale parameters. Consequent wave numbers increase/decrease, accompanied by decreasing/increasing number of wavelengths, thereby further justifying the shallow segment representation employed herein.

Analysis of Stiffened Penstock External Pressure Stability Based on Immune Algorithm and Neural Network

The critical external pressure stability calculation of stiffened penstock in the hydroelectric power station is very important work for penstock design. At present, different assumptions and boundary simplification are adopted by different calculation methods which sometimes cause huge differences too. In this paper, we present an immune based artificial neural network model via the model and stability theory of elastic ring, we study effects of some factors (such as pipe diameter, pipe wall thickness, sectional size of stiffening ring, and spacing between stiffening rings) on penstock critical external pressure during huge thin-wall procedure of penstock. The results reveal that the variation of diameter and wall thickness can lead to sharp variation of penstock external pressure bearing capacity and then give the change interval of it. This paper presents an optimizing design method to optimize sectional size and spacing of stiffening rings and to determine penstock bearing capacity coordinate with the bearing capacity of stiffening rings and penstock external pressure stability coordinate with its strength safety. As a practical example, the simulation results illustrate that the method presented in this paper is available and can efficiently overcome inherent defects of BP neural network.

Buckling Analysis of a Super-Large Storage Tank

In this paper, buckling analysis was carried out on a super-large storage tank under uniform external pressure or wind pressure with finite element method. The critical pressures and buckling deformation modes are obtained and the effects of wind girders and reinforcing rings are investigated. It is found that the critical external pressure of the tank under uniformly applied external pressure obtained by the eigenvalue method is smaller than that obtained by the nonlinear method. Buckling only occurs on the windward side of the tank under the wind pressure. As strengthened by the wind girders and reinforcing rings at the upper par of the tank, buckling deformations here are much smaller than those at the lower part of the tank.

First-Ply Strength of Thick Circular Cylindrical GRP Composite Shell Subjected to Static External Pressure via Finite Element Simulation and Analytical Approaches

One-ply thick externally pressurized GFRP cylinders were analyzed using computational numerical simulation and analytical method. The main part of the work was to study the critical external pressure to avoid failure in the laminated shells by employing various phenomenological failure criteria. Comparison between ABAQUS FEM simulation results and analytical solutions using MATLAB programming codes proved high accuracy of the analytical approach. Various fiber angles stacking sequences were chosen for optimization analysis. The results did not show any increase in stability as the layer number increased. The results also showed high correlation with corresponding failure criteria. The analytical solutions gave higher accuracy as the number of plies and the total laminate thicknesses were reduced.

Riser Stability Under External Pressure and Axial Compression Observing Geometrical Imperfections

Steel pipes are studied considering external pressure, axial compression and bending actions to empty condition, taking into account the initial geometrical imperfections. The main objective is to study the behavior and structural stability of these pipes submitted to combine loads, considering the influence of the geometrical imperfections and to estimate the critical external pressure. Critical pressure of buckling, and modal configurations are evaluated by theoretical methods and numerical approaches such as finite element method (FEM). The numerical results are compared with theoretical results.