195 Vessel for dangerous liquid waste treatment calculation The presented project is about the realisation of special small vessels for very dangerous nuclear waste treatment. This project includes more than twenty different apparatus which were produced by the Slovak company TECHNOS Ltd. The main task for our firm was to perform the structural calculation of the vessel shells, nozzles and anchoring of the vessels. The input for the calculations was taken from data sheets and from the shop drawings of the vessels. All designed tanks were also checked for seismic resistance. The main aim of the calculations was to calculate the internal force stresses: in test condition, in normal operation and extraordinary operation, including also seismic effects. Structural calculation The design of the vessel is always connected with the use of relevant codes like ASME, AD-Merkblat and Eurocodes. Relevant codes usually calculate the mechanical resistance of the parts of the vessel with some influence of the connected parts. The advantage of such an approach is a relatively simply calculation based on formulas. The accuracy of such an approach depends on the shape and on the character of the loads. For the calculation of the vessels with different shapes and different loads as mentioned in the code, we can use a similar vessel. For the calculation of such “uncommon “ vessels we can use the finite elements method. Computational model Vessel shells are modelled by shell elements and legs and other supporting parts are modelled by beam elements. The modelling of the main parts is clear. An important task is how to model the connection of the parts as reinforcing plates, rings and collars by welds. The reinforcing part is connected with the shell, which is reinforced only in the part of the welds. The connection of the parts could be modelled as part of the shell, which is perpendicular to main shape. In this case we can use intersections of the shells very effectively. Intersection of the shells in the ESA-Prima Win and SCIA•ESA PT is a very effective tool for the modelling of the vessel. Without these tools it is unimaginable to create a computational model of the vessel where nozzles connections supports reinforcing parts. Method of calculation Calculations of the seismic response of the vessel with liquid inside can be performed by two approaches, firstly a time history response on the accelerogram. The liquid in this case is modelled by fluids elements. Secondly we can use the linear response spectra method for the calculation of the forces in the supporting parts and quasi-static method for calculation vessel shells. Important for this approach is to use appropriate modelling of the liquid. Part of the liquid inside of the vessel has to move unisons with the vessel (impulsive mass) and a smaller part of the mass moves independently on the vessel (convective mass). The first portion of the liquid mass can be modelled as a mass connected with the shell. The second part can be modelled as elastically connected with the shell by the springs. The system of the springs has to have the same frequency as calculated by the code. From the analysis of the system by linear response spectra we received internal forces and stresses in the shell. It is important where the anchoring points of the vessel are located. Modal shapes and own frequency of vibration are important for the bending mode approximation. On the basis of the frequency of the bending mode of vibration, we are able to approximate seismic acceleration. Method of checking Stresses in the shell are compared with stresses allowed by codes. As is known in the location of singularities the stresses are very high. For singularity problems solution we used formulas mentioned in codes and check the stresses accordance with the codes. Very important is origin of the stresses. Different values are allowed for stresses from bending moments a different from membrane forces. Software use Calculation was performed by ESA-Prima Win. MathCad 2001 Professional was used to perform additional calculation. Obtained result & conclusions Internal forces stress deformation and also modal parameters of the vessel were obtained from calculation. Without usage of the complex model of the vessel the results would not be so precise. Based on this calculation, the vessel was checked according to the code. Vessel for dangerous liquid waste treatment calculation The presented project regards the design of special small vessels for very dangerous nuclear waste treatment. It includes more than twenty different apparatus which were produced by the Slovak company TECHNOS Ltd The structural analysis of the vessels is performed by a combination of the FEM method and the analytical method. For the shell, the modelling intersection modulus of ESA-Prima Win is used. The seismic response is solved by the linear response spectra. Stresses in the shells are checked according to the codes.
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