Nemetschek Engineering User Contest 2009 • Category 5: CAE Special Projects 185 5 ACO Clara sewage treatment plant as return sludge and also partly into the storage area as surplus sludge. The final sedimentation tank is optionally equipped with a skimmer for the automatic collection and removal of floating sludge from the water surface. This device reduces maintenance work during the operation. Used Modules • Linear static analysis of complicated shells • Intersections • Stability of shells • Geometrical Nonlinearity • Intelligent document Analysis description Plastics structures exhibit a viscoelastic behaviour, dependent on time of load exposition, temperature and stress level reached in the material. The analysis of the thermoplastics starts with the long term strength and creep modulus determination. The number of analysis necessary is then related to these conditions. In case of scrubber 2 crucial states were defined – working state and the short term loads states. Both states have the same geometry and model of the construction but differ in the modulus of elasticity and in the allowable stresses. As a result 2 independent linear analyses and 2 stability analysis were performed. 2 documents are enclosed. Experience The design of thermoplastic process equipment, using the appropriate design parameters and material properties can be completed with a combination of hand calculations and computer run Finite Element Analysis (FEA). FEA is necessary to determine peak stresses at discontinuities, corner joints, and to verify strain limits etc. For a complete FEA analysis to be executed for thermoplastic process equipment, a non-linear analysis should be accomplished. However, this is usually impractical due to time, lack of detailed material strength design data, and the relatively low allowable design stresses used. Satisfactory designs have been consistently accomplished by using a linear elastic FEA approach and by using a constant on required years of durability dependent creep modulus value for the design allowable stresses. Measurements of fabricated thermoplastic structures indicate the linear elastic approach to be a viable and relatively accurate prediction of equipment stresses and deformations. Conclusion Complicated shapes of thermoplastic vessels require powerful tools for simplifying the geometry creation – intersections are the necessity. Several linear solutions of the structure varying in creep modulus in relationship to the temperature, time of load exposition and the stress level reached must be analysed. Each of the linear analysis must also be complemented by the stability check of the construction for the same creep modulus value. Sometimes the stability analysis does not give the positive values of the critical factors, depending on the geometry, loads and supports. Then the geometrical nonlinear analysis must be used to find out the remaining load bearing capacity of the structure, several nonlinear analyses with regularly increased loads have to be performed till the collapse of the solver gives the critical load factor value. The number of equations solved normally varies between 100.000 – 1,000.000. So the requirements for really fast solver are great, mostly the iterative solver takes place. All above mentioned features are included in ESAPrima Win software, the best solution for FEA of the thermoplastics vessels I have ever used.
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