| Oil cooler is a kind of compact heat exchanger, and it has a lot of advantages, such as high heat-conducting capacity, small volume, low weight, easy to design and fix. So it has been applied widely to cool down the lubricant in automobile and construction engines. And its quality determines a lot to the performance of engines. On the other hand, the working environment of oil cooler is rather tough, such as long term work of the engine, intense vibration, contaminated lubricant, transient pulse force in lubricating system, etc. As a result, the heat exchanger tends to break down due to alternating load. It is quite necessary to carry out fatigue life-span test on oil cooler during its development and production.A fatigue test machine for oil cooler was developed based on DCS (Distribute Control System) in this paper. Pressure accuracy in the system contributes greatly to the test results. In addition, the device is expected to be versatile, so it can fit for experiments on series of products and different test parameters. To meet this demand, the test machine must have a strong self-tuning ability. Furthermore, the test machine must also be robust to some uncertain parameters and disturbance. A repetitive control system was designed to achieve above requests, the simulation model was created in Matlab to check out its work. Another feature of this thesis is to investigate the inner pressure in heat exchanger. It's hard to get the data in common test machines, for pressure sensors can only be fixed at the inlet or outlet of closed frame test piece. Thanks to computational fluid dynamics, it can be predicted based on a mathematical model derived from simulation results. The study on the inner pressure of heat exchanger can also serve to its development, which has a great influence on heat-conducting capability and construction safety.Main contents of this thesis are listed as below:(1) Function of oil cooler and basic principles of fatigue life-span and fatigue test machine were introduced, and main construction and features of electro-hydraulic control system were summarized, as well as some cutting-edge electro-hydraulic servo control strategies. (2) A group of fruits of other fatigue test machines were studied as reference to this one. In order to check the work of advanced control strategy, main structure of the test machine was built up.(3) Inner friction property of heat exchanger, CFD technology and multi-porous media theory were learned, and then oil cooler cores were transformed and treated as multi-porous media model.(4) Simulation model of heat exchanger was built up in Gambit, and simulation was carried out in Fluent. The pressure distribution law was derived by analyzing the results and polyfitting the data in Matlab.(5) One particular advanced control strategy was appointed according to demands and properties of the test machine, next step was to learn its theory and applications in servo systems. Repetitive control was an ideal candidate for the test machine in this thesis.(6) Model of electro-hydraulic system and some properties were gained, and simulation model was created in Matlab.(7) Repetitive controller was created in state-space method, and then repetitive control system was also built up in Matlab, and then some simulation experiments were done to check the functions of the controller. Some experiences in design and analysis of repetitive were summarized, which can be referred by other applications. |
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