Nestacionarna strujanja u sistemima za transport tečnosti i njihova zaštita

Abstract

The subject matter of this dissertation is a general analysis of unsteady flows in hydraulic transport pipelines with a special focus on small hydropower pipelines and the determination of dynamic properties of control valves and the stator. The determined dynamic properties of governors and system behavior are verified through comparison with the measured results. The research subject and aims are defined based on the analysis of previous relevant literature. Mathematical modelling of unsteady fluid flow in pipelines is conducted. The speed of pressure disturbance during water hammer is determined and some basic cases of this phenomenon are presented. Based on the review of available methods that significantly contributed to the study of this phenomenon, the method of characteristics is deductively selected to solve the relevant differential equations with boundary and initial conditions, after which different representations of the friction factor are given. Based on market availability of different valve types, three of them are selected; calculations and analyses of the three valves yielded results that were then used to propose the best valve type water hammer mitigation. Afterward, the basic parameters of water turbines are described and a classification is provided for the turbines, for which linear and universal characteristics are then determined according to the main universal characteristic and the use of universal characteristics to obtain Suter curves is demonstrated. Water hammer is modelled for systems containing a Pelton and a Francis turbine and the results for specific small hydropower plants are then verified against the modelling results. The dissertation also discusses potential static and hydrodynamic methods of leakage detection in hydraulic transport systems, with special focus on the method of pressure gradient analysis, which is then supplemented with unsteady analyses for intentionally created pressure disturbances in the system. Based on the developed models for establishing the dynamic properties of transients, a procedure is proposed for identifying leakage and leakage locations in a hydraulic system. The obtained results will be used to formulate recommendations for improved reliability and system protection.