Stress Analysis Of Egg-Shaped Sludge Digester And Shape Optimization Based On Genetic Algorithm

Compared to the traditional cylindrical digesters, the egg-shaped sludge digestersbehave well in mechanical performance with its shape fitting the specificrequirements of technical process in environmental engineering. The egg-shapedsludge digesters have been set up in many countries;however, their widespreadadoption is hampered in China by the lack of detailed and systematic analysis.First of all, based on the theory of classical elastic shell theory, an egg-shapedsludge digester computation model is established taking the hydrostatic pressure asthe primary load. The model is made up of two cones and the middle egg shaped shell.The thickness is assumed to be a constant. The support is assumed continuouslydistributed under the digester.The membrane stresses and deformations of egg-shaped sludge digester areevaluated by membrane theory. Parametric studies are conducted on the basis of theseanalytical results. The bending stresses and deformations of the junction and supportunder bending effects are calculated by compatibility condition. Total stresses willthen follow by superimposing the membrane stresses. An FEM model based on theabove analytical model in ANSYS is made to compare. The model of egg-shapedsludge digester in Jining Southern Suburb Sewage Farm is calculated.Based on the above results, an optimization model with object function andconstraint conditions is established. A genetic algorithm optimization procedurecombined with the dynamic penalty function is adopted. The constraint conditions areapproximated gradually to find the feasible and optimum solutions. Designrecommendations proposed for egg-shaped sludge digesters are presented.