Search

Health condition monitoring of rotating machinery is a crucial task to guarantee reliability in industrial processes. In particular, bearings are mechanical components used in most rotating devices and they represent the main source of faults in such equipments; reason for which research activities on detecting and diagnosing their faults have increased. Fault detection aims at identifying whether the device is or not in a fault condition, and diagnosis is commonly oriented towards identifying the fault mode of the device, after detection. An important step after fault detection and diagnosis is the analysis of the magnitude or the degradation level of the fault, because this represents a support to the decision-making process in condition based-maintenance. However, no extensive works are devoted to analyse this problem, or some works tackle it from the fault diagnosis point of view. In a rough manner, fault severity is associated with the magnitude of the fault. In bearings, fault severity can be related to the physical size of fault or a general degradation of the component. Due to literature regarding the severity assessment of bearing damages is limited, this paper aims at discussing the recent methods and techniques used to achieve the fault severity evaluation in the main components of the rolling bearings, such as inner race, outer race, and ball. The review is mainly focused on data-driven approaches such as signal processing for extracting the proper fault signatures associated with the damage degradation, and learning approaches that are used to identify degradation patterns with regards to health conditions. Finally, new challenges are highlighted in order to develop new contributions in this field. [ABSTRACT FROM AUTHOR]

The focus in mutation testing is on the elimination of first-order mutants. It is widely believed that there is a coupling effect between first-order and higher-order mutants such that a test set that kills the former would be expected to kill the latter too; it follows that, if the belief is correct, there is no need whatsoever to bother with higher-order mutants. It turns out, in practice, that most higher-order mutants do get killed by such a test set, though a few somehow manage to survive.This is the first of two papers dealing with the coupling effect from a theoretical standpoint. The overall results indicate that the hypothesis of a coupling effect is largely valid, provided the program is not too large; only a tiny proportion of higher-order mutants is expected to survive a test set that kills all first-order mutants. The basis of the approach is that programs can be modelled as compositions of finite functions, the domain of which is assumed to be large.The problem is a complex one, so the present paper only considers the case where there is just one test data; the case where there are more than one test data is left to a second paper. The aim is not only to show that the coupling effect actually exists, but also to gain some understanding of the various factors underlying it. [Copyright &y& Elsevier]

Estimating the additional power losses caused by an inter-laminar short circuit in electromagnetic devices using thermal measurements depends on many parameters such as thermal conductivity, heat capacity, convective heat coefficient, and size of the fault points. This paper presents a method for estimating these parameters using experimental measurement and a numerical model. The surface temperature rise due to inter-laminar short circuit fault was obtained using an infrared camera. Based on the initial temperature rise method, the least square non-linear approximation technique was used to determine the best fitting parameters of the fault region from the numerical model. To validate the results obtained, the fault region temperature rise and the total loss of the experimental sample were compared with the numerical model using the obtained parameters for different current supply conditions. The study shows that surface temperature distribution can be used to estimate the inter-laminar short circuit fault parameters and localized losses. [ABSTRACT FROM AUTHOR]