Elephant Foot Buckling Analysis of Large Unanchored Oil Storage Tanks With Tapered Shells Subjected to Foundation Settlement

This paper presents an numerical study on a large unanchored open-topped steel tank. The buckling behaviors of the tank are analyzed using the finite element computer package ANSYS by means of nonlinear stabilization algorithm. The effects of foundation harmonic settlement on the elephant foot buckling strength of large unanchored open-topped oil storage tanks with tapered shells under axial compression are explored by numerical modeling. Various items of actual geometrical structure which involve concrete ringwall foundation of tank, unanchored bottom with slope, shell tapering from the base to the top, wind girders and supports, top angles, stiffening rings and support plates are presented thoroughly in the non-symmetrical 3D finite element model. Geometric nonlinearity, nonlinear boundary conditions and elastic plastic material of Ramberg-Osgood model are involved simultaneously in simulate course. The obtained solutions are displayed graphically for selected values of system parameters: harmonic settlement amplitude, harmonic number, and critical buckling stress of axially compressed oil tank. The results will provide insights into the relationship between foundation harmonic settlement and buckling strength of the large cylinders.

Nonlinear control design using Takagi-Sugeno fuzzy applied to under-actuated visual servo system

This paper presents the Takagi-Sugeno (TS) fuzzy control design for nonlinear stabilization and tracking control of a ball on plate system. To deal with the plant nonlinearity and the fuzzy convergence issue, we formulate the parallel distributed compensator (PDC) TS fuzzy model to characterize the global behaviour of the nonlinear system and synthesize a feasible control framework using a velocity compensation scheme. The nonlinear dynamics of the ball on plate system is obtained using the Euler-Lagrangian energy based approach. To identify the moving objects in the video stream, a background subtraction algorithm using thresholding technique is formulated. Moreover, the stability analysis of the TS fuzzy control is reduced to linear matrix inequality (LMI) problem and solved using the Lyapunov direct method. The potential benefits of the proposed control structure for real time test cases are experimentally assessed using hardware in loop (HIL) testing on a ball on plate system. Experimental results substantiate that the TS fuzzy scheme can significantly improve not only the tracking performance but also the robustness of the closed loop system.