Fusing neural networks, genetic algorithms and fuzzy logic for diagnosis of cracks in shafts

During the last decades, the engineering community has extensively studied crack identification in rotating machine elements. Although the proposed analytical models may be capable of identifying cracks on the basis of modal analysis, response easurements or other techniques, the required time for performing the underlying computations is restrictive in real-time diagnosis applications. This paper introduces a framework for implementing soft-computing techniques, namely artificial neural networks (ANN), fuzzy logic (FL) and genetic algorithms (GA), for identifying cracks in rotating shafts while diminishing the required computational time. In the context of the current approach the cracks are considered to lie on arbitrary angular positions around the longitudinal axis of the shaft at any distance from the clamped end and characterized by three measures: position, depth and relative angle. The reduction in computational time is achieved by approximating the analytical model with a neural network and by replacing the exhaustive search of the solution space with a genetic algorithm whose objective function relies on a fuzzy logic representation. Results concerning the efficiency of the proposed framework in terms of accuracy and computational time are also presented.

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Submitted by ashraf_afify on Mon, 03/07/2006 - 3:02pm.

Hi,

The framework introduced for identifying cracks in rotating shafts is interesting. I have one query: You mentioned in the abstract that the reduction in computational time is achieved by .. and by replacing the exhaustive search of the solution space with a genetic algorithm.. What sort of search techniques do genetic algorithms use?

Thank you,
Afify

Submitted by gebalan on Sat, 08/07/2006 - 8:24am.

Hello,
Please tell me what possibilities exist for experimental verification of these results.
Sincerely,

Submitted by Pham on Sun, 09/07/2006 - 8:29pm.

Hi Afify: As far as I know, GAs implement a form of stochastic search guided by gradient information. Best wishes. DTP.

Submitted by Pham on Sun, 09/07/2006 - 8:44pm.

Hello Professor Dentsoras,
Thank you for your paper.
I would be interested to know if you think our
Bees Algorithm would work in your application.
Best wishes.
DTP.

Submitted by Dentsoras on Mon, 10/07/2006 - 8:59am.

Hi afify,

The genetic algorithms search the solution space by using the output of an objective function on a evolutionary basis, thus the genetic algorithm may provide optimal solutions very fast without the need of searching all the solution space. The alternative methodology is to utilize an exhaustive optimization search, which increases the values of the related objective function’s variables by a small pre-defined step. In our study-case the second alternative cannot provide a solution by using a normal step in a optimization time less than 3 days, thus this cannot be considered for a real-time crack diagnosis system.

Regards,

Argiris Dentsoras

Submitted by Dentsoras on Mon, 10/07/2006 - 9:03am.

Hi gebalan,

The deployment of the GA together with neural network approximation of the multi-crack identification model is capable of delivering results in remarkable time periods (e.g. 5 mins) and with high efficiency. The experimental verification of the results should be applied mostly in the context of the cracks identification model. Several experiments have been performed and it seems that the model validates the experimental values. An experimental validation of the cracks identification model is carried out as follows: a) two cracks of different attributes (depths, position, angle) are created on a shaft, b) the shaft begins to rotate and the responses are measured at four points, c) the analytical cracks identification model is deployed and the taking as input the responses and estimating the cracks attributes. It is evident that each experiment is quite time-consuming and that each shaft can be used for specific cracks positions and angles and only depths can be varied during each experiment.

Best regards,

Argiris Dentsoras

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