MECHANICS OF MACHINES AND MECHANISMS - MODELS AND MATHEMATICAL METHODS
Plan rada Seminara Mehanika mašina i mehanizama - modeli i matematičke metode za MART 2020.
UTORAK, 03.03.2020. u 17:00, Sala 301f, MI SANU, Kneza Mihaila 36
Stepa. M. Paunović, Mathematical Institute SANU, Belgrade, Serbia
SOME PROBLEMS AND POSSIBLE SOLUTIONS IN MATHEMATICAL MODELLING OF A PIEZOELECTRIC DYNAMIC ABSORBER
Piezoelectric dynamic absorbers (PEDA) can be used to effectively attenuate vibrations of the primary structure while transforming the mechanical energy of these vibrations into electrical energy, thus acting both as dynamic absorbers and energy harvesting systems. These systems are very suitable for application to a broad range of civil engineering structures, such as tall buildings or long-span bridges, where vibrations induced by exploitation loads or wind can be severe. In this way not only that the vibrations are mitigated, but also the electricity generated during this process can be used to power lights or structural health monitoring devices, thus contributing to development of smart structures and integral systems. Therefore it is important to formulate a precise, reliable and robust mathematical model for design and analysis of PEDA. In this lecture, the basic design and modelling concepts of one type of piezoelectric dynamic absorber, derived in the ongoing research within the lecturer’s PhD thesis, will be presented. First, the basic types of dynamic absorbers and piezoelectric energy harvesters will be briefly described, providing the background for understanding the main ideas regarding the proposed design variant of PEDA which follow. Next, the derived mathematical model will be examined in detail, pointing out the problems encountered during the modelling procedure, as well as the means and methods used to solve them. Finally, the planned optimization of the proposed model will be briefly discussed, concluding with the future outlooks and possibilities for further development of the presented model.
UTORAK, 17.03.2020. u 17:00, Sala 301f, MI SANU, Kneza Mihaila 36
Ana Petrović, Faculty of Mechanical Engineering, University of Belgrade, Serbia
MEHODS FOR NUMERICAL AND EXPERIMENTAL DIAGNOSTICS OF COMPLEXE STRUCTURES’ STRENGTH-WITH SPECIAL REFERENCE TO MODEL ANALYSIS
There are numerous examples of failure of steel structures. There are various causes, such as error in design, error in production, error in exploitation or unexpected loads. When failure occurs, standard series of operations should be performed. Solving the problem most often requires numerical and experimental analysis that is applied iteratively. Inevitable is performing numerical calculation of the structure, using well-known FEM analysis. In principle, if stress concentrations coincide with locations of cracks, this indicates a bad design solution and proposal for redesign of the structure should be given. However, stress is not the only indicator of defect in design. It is necessary to know free frequencies of the structure, and distribution of potential and kinetic energy in the main modes of oscillation. Reanalysis method and dynamic modification are procedures based on different relations between potential and kinetic energy, and gives recommendations for redesign. The main objective of a dynamic modification of the structure is to increase the first frequency of oscillation, and that the gap between adjacent frequencies is as big as possible, but this method can be used to reduce the stress concentration as well. Several examples of everyday engineering practice will show the importance of reanalysis method, and that it can be applied to all types of structures, from very simple to complex. Considering experimental approach, possibilities of performing experiments on real constructions are often limited, especially in case of large constructions. One of the solutions is to create a sub-scaled model in order to anticipate the behavior of the real construction, regarding the behavior of the model, with sufficient accuracy. So, the idea is making a sub-scaled model of the construction itself, which will provide the possibility of numerical-experimental "learning" about the strength and rigidity of this construction. Advantages of model testing will be shown by example of the bucket wheel excavator substructures. Model testing includes: (1) creating sub-scaled model (physical and numerical), (2) assessment of load applied to model using recommendations given by similarity method, (3) performing (static and dynamic) numerical calculations of a real construction and its sub-scaled model, and formulating of coefficients connecting these two models, (4) performing experiments of a model in order to verify all the numerical models. Also, model testing allows testing in a laboratory "clean" environment, which also allows the application of sensitive test equipment, such as system for non-contact stress and strain measurement based on Digital Image Correlation (Aramis system).
Predavanje se odlaže zbog trenutne epidemiološke situacije u zemlji. Novi termin predavanja biće utvrđen u dogovoru sa predavačem nakon prevazilaženja trenutne situacije.
Seminar Mehanika mašina i mehanizama - modeli i matematičke metode započeo je sa radom u junu 2018.god. Seminar se održava do dva puta mesečno, utorkom u periodu od 17.00 - 19.00 u Matematičkom institutu SANU.
dr Ivana Atanasovska