Mass unbalance, shaft misalignment, rotor asymmetry, and force due to rotor weight are the main causes of vibrations in rotary machines especially when the shaft is not symmetric. Although extensive researches have been carried out to determine the effect of each on the increase of vibration levels far, there has been no clear study on the simultaneous existence of all these parameters and their interactions. In this research, the model is a rotor composed of a rigid disk and a flexible asymmetric shaft. The general equations of motion are first derived by considering the effect of high order large deformation in bending. The equations are discretized using the Rayleigh–Ritz method. The obtained equations are nonlinear coupled differential equations that are solved using the numerical method. Sensitivity analysis has been utilized to identify the percentage of the contribution of each parameter to the increase of vibration. Then a DOE-based Response Surface Methodology (RSM) is applied to present a model to predict the vibration behavior of the system with good accuracy. Genetic algorithm is also used to optimize the effective parameters and to verify the results. A 3D model of the asymmetric rotor is carried out in experimental studies to attain more precise responses. The research shows that rotor asymmetry alone and also its combination with gravitational force has much more effects on the vibration amplitude. These effects are observed at frequencies both once and twice the rotational speed in spectral data, in comparison with other factors. The mass unbalance also plays a significant role in frequency equal to the rotational speed. In the end, the achieved results are validated with experimental simulations.
The efficiency of the ventilation system is a key point for durable and reliable electric generators. The design of such system requires a detailed understanding of the air flow in the generator. Computational fluid dynamics (CFD) has the potential to resolve the lack of information in this field. The present work analyses the air flow inside a generator model. The model is designed using a CFD-based approach, and manufactured by taking into consideration the experimental and numerical requirements and limitations. The emphasis is on the possibility to accurately predict and experimentally measure the flow distribution inside the stator channels. A major part of the work is focused on the design of an intake and a fan that gives an evenly distributed flow with a high flow rate. The intake also serves as an accurate flowmeter. Experimental results are presented, of the total volume flow rate, the total pressure and velocity distributions. Steadystate CFD simulations are performed using the FOAM-extend CFD toolbox. The simulations are based on the multiple rotating reference frames method. The results from the frozen rotor and mixing plane rotor-stator coupling approaches are compared. It is shown that the fan design provides a sufficient flow rate for the stator channels, which is not the case without the fan or with a previous fan design. The detailed experimental and numerical results show an excellent agreement, proving that the results reliable.
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