Rubber sealing ring is one of the most widely used seals. It is always stored for a period of time before put into use, especially in aeronautic and aerospace applications. It is necessary to ...evaluate the storage lifetime of rubber sealing rings. However, due to the long storage lifetime of rubber sealing rings, two issues need to be handled, including model uncertainty and lack of storage lifetime data. A Bayesian model averaging based storage lifetime assessment method for rubber sealing rings is proposed in this article. The Gamma distribution model and Weibull distribution model are selected as the candidate models and combined based on Bayesian model averaging method. The Bayesian model averaging method is applied to handle the model uncertainty. Considering the lack of storage lifetime data, the degradation data are utilized to give the priors of model probability and distribution parameters based on the similarity principle. The results indicate that the proposed method has smaller minus log-likelihood value and is better than the other discussed method, considering both goodness of fit and complexity.
Actuation system is a vital system in an aircraft, providing the force necessary to move flight control surfaces. The system has a significant influence on the overall aircraft performance and its ...safety. In order to further increase already high reliability and safety, Airbus has imple- mented a dissimilar redundancy actuation system （DRAS） in its aircraft. The DRAS consists of a hydraulic actuation system （HAS） and an electro-hydrostatic actuation system （EHAS）, in which the HAS utilizes a hydraulic source （HS） to move the control surface and the EHAS utilizes an elec- trical supply （ES） to provide the motion force. This paper focuses on the performance degradation processes and fault monitoring strategies of the DRAS, establishes its reliability model based on the generalized stochastic Petri nets （GSPN）, and carries out a reliability assessment considering the fault monitoring coverage rate and the false alarm rate. The results indicate that the proposed reli- ability model of the DRAS, considering the fault and redundancy degradation process and identify monitoring, can express its fault logical relation potential safety hazards.
This paper proposes an active fault-tolerant control strategy for an aircraft with dissimilar redundant actuation system （DRAS） that has suffered from vertical tail damage. A damage degree ...coefficient based on the effective vertical tail area is introduced to parameterize the damaged flight dynamic model. The nonlinear relationship between the damage degree coefficient and the corresponding stability derivatives is considered. Furthermore, the performance degradation of new input channel with electro-hydrostatic actuator （EHA） is also taken into account in the damaged flight dynamic model. Based on the accurate damaged flight dynamic model, a composite method of linear quadratic regulator （LQR） integrating model reference adaptive control （MRAC） is proposed to reconfigure the fault-tolerant control law. The numerical simulation results validate the effectiveness of the proposed fault-tolerant control strategy with accurate flight dynamic model. The results also indicate that aircraft with DRAS has better fault-tolerant control ability than the traditional ones when the vertical tail suffers from serious damage.
Accurate reliability estimation for reciprocating seals is of great significance due to their wide use in numerous engineering applications. This work proposes a reliability estimation method for ...reciprocating seals based on multivariate dependence analysis of different performance indicators. Degradation behavior corresponding to each performance indicator is first described by the Wiener process. Dependence among different performance indicators is then captured using D-vine copula, and a weight-based copula selection method is utilized to determine the optimal bivariate copula for each dependence relationship. A two-stage Bayesian method is used to estimate the parameters in the proposed model. Finally, a reciprocating seal degradation test is conducted, and the proposed reliability estimation approach is validated by test data. Results show that the proposed model is accurate and effective in estimating the reliability of reciprocating seals.
Passive dew harvesting and rainwater collection requires a very small financial investment but can exploit a free, clean (outside urban/industrial zones) and inexhaustible source of water. This study ...investigates the relative contributions of dew and rain water in the Mediterranean Dalmatian coast and islands of Croatia, with emphasis on the dry summer season. In addition, we evaluate the utility of transforming abandoned roof rain collectors (“impluviums”) to collect dew water too. Two sites were chosen, an exposed open site on the coast favourable to dew formation (Zadar) and a less favourable site in a cirque of mountains in Komiža (Vis Island). Between July 1, 2003 and October 31, 2006, dew was collected two or three times per day on a 1 m
2 inclined (30°) test dew condenser, together with standard meteorological data (air temperature and relative humidity, cloud cover, windspeed and direction). Maximum yields were 0.41 mm in Zadar and 0.6 mm in Komiža. The mean yearly cumulative dew yields were found to be 20 mm (Zadar) and 9.3 mm (Komiža). Because of its physical setting, Komiža represents a poor location for dew collection. However, during the dry season (May to October), monthly cumulative dew water yield can represent up to 38% of water collected by rainfall. In both July 2003 and 2006, dew water represented about 120% of the monthly cumulative rain water. Refurbishing the abandoned impluviums to permit dew collection could then provide useful supplementary water, especially during the dry season. As an example, the 1300 m
2 impluvium at Podšpilje near Komiža could provide, in addition to rain water, 14,000 L dew water per year.
Mechanical debris is an important product of friction wear, which is also a crucial approach to know the running status of a machine. Many studies have been conducted on mechanical debris in related ...fields such as tribology, instrument, and diagnosis. This paper presents a comprehensive review of these studies, which summarizes wear mechanisms (e.g., abrasive wear, fatigue wear, and adhesive wear) and debris features (e.g., concentration (number), size, morphology, and composition), analyzes detection methods principles (e.g., offline: spectrograph and ferrograph, and online: optical method, inductive method, resistive-capacitive method, and acoustic method), reviews developments of online inductive methods, and investigates the progress of debris-based diagnosis. Finally, several notable problems are discussed for further studies.
The dew equipment for water project in Bisevo was presented. A project Dew Equipment for Water (DEW) was initiated for a 15.1 super(2) roof in the island of Bisevo equipped with commercial plastic ...cover selected for its superior dew collection properties. Measurements of both rain and dew water would be performed over several years and data would be correlated with meteorological data collected in situ. Preliminary measurements during the period 21 April-21 October 2005 showed that dew water contributed significantly, 26% of the total collected water. It was found that the dew occurred on a very regular basis. The cumulated rain water amounted to 642 L and the dew water to 222 L.
•Model and parameter uncertainties are considered in statistical analysis.•Evidence theory is introduced to fuse candidate degradation process models.•Difference of goodness-of-fit of candidate ...models is considered.•Inferenced results are precise and stable under small sample size conditions.•The proposed method is still effective under small sample size conditions.
Several methods have been proposed to handle uncertainty issues, including process uncertainty and parameter uncertainty, in stochastic-process based degradation modeling and statistical analysis. However, these methods oftentimes do not address the uncertainty issues well under small sample conditions. Hence, due to the powerful ability of evidence theory to describe uncertainty, especially under small sample conditions, an evidence theory based model fusion method is proposed. The candidate models are considered as different evidence sources and give evidences about the evaluated product based on likelihood. Considering the heterogeneous characteristics of the evidences predicted from different candidate models, the reliability degree is introduced to convert the evidences and estimated based on goodness-of-fit. By fusing converted evidences, inferences and estimations of reliability, degradation mean, degradation variance, and mean time to failure are obtained. The effectiveness of the proposed method is verified by previously published degradation datasets and comparing to Bayesian model averaging method and model selecting method. The degradation mean and variance estimations are more precise and more stable compared to the other two methods under small sample conditions. Furthermore, the proposed method can be used to consider the uncertainty issues by belief, plausibility and uncertainty measure, even though under extremely small sample conditions.
Directing to the high cost of computer simulation optimization problem, Kriging surrogate model is widely used to decrease the computation time. Since the sequential Kriging optimization is time ...consuming, this article extends the expected improvement and put forwards a modified sequential Kriging optimization （MSKO）. This method changes the twice optimization problem into once by adding more than one point at the same time. Before re-fitting the Kriging model, the new sample points are verified to ensure that they do not overlap the previous one and the distance between two sample points is not too small. This article presents the double stopping criterion to keep the root mean square error （RMSE） of the final surrogate model at an acceptable level. The example shows that MSKO can approach the global optimization quickly and accurately. MSKO can ensure global optimization no matter where the initial point is. Application of active suspension indicates that the proposed method is effective.
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