Wind Power Performance Optimization Considering Redundancy and Opportunistic Maintenance

In This paper the redundancy and imperfect opportunistic maintenance optimization of a multi-state weighted k-out-of-n system is formulated. The objective is to determine the k-out-of-n system redundancy level and the maintenance strategy which will minimize the wind farm life cycle cost subject to an availability constraint. A new condition based opportunistic maintenance approach is developed. Different component health state thresholds are introduced for imperfect maintenance of failed subsystems and working subsystems and preventive dispatching of maintenance teams. In addition, a simulation method is developed to evaluate the performance measures of the system considering different types of subsystems, maintenance activation delays and durations, limited number of maintenance teams, and discrete inspection of the system. Also, a multi-seed tabu search heuristic algorithm is also proposed to solve the formulated problem. An application to the optimal design of a wind farm is provided to illustrate the proposed approach

Condition based maintenance optimization for multi-state wind power generation systems under periodic inspection

As the wind power system moves toward more efficient operation, one of the main challenges for managers is to determine a cost effective maintenance strategy. Most maintenance optimization studies for wind power generation systems deal with wind turbine components separately. However, there are economic dependencies among wind turbines and their components. In addition, most current researches assume that the components in a wind turbine only have two states, while condition monitoring techniques can often provide more detailed health information of components. This study aims to construct an optimal condition based maintenance model for a multi-state wind farm under the condition that individual components or subsystems can be monitored in periodic inspection. The results are demonstrated using a numerical example.info:eu-repo/semantics/publishedVersio

Comparing Hysteretic Energy and inter-story drift in steel frames with V-shaped brace under near and far fault earthquakes

Different researches have shown that during destructive earthquakes, most structures enter non-reactionary range. Hysteretic Energy, which is wasted after the yield within its hysteresis rings, is very influential on generating structural damage of the system, being the most important component in the equation of the energy, inflicted on the structures. Therefore, controlling this amount of energy leads to controlling the structure behavior. The amount of Hysteretic Energy in a structure could be an index of its damage level or its malleability. The current paper carries out a nonlinear dynamic analysis on steel buildings with a V-shaped (Chevron) brace, hence surveying Hysteretic Energy distribution as well as maximum inter-story drift in the stories of these buildings, under the influence of equalized near and far fault records. Results show that the inter-story drift need for equalized near fault records is more than the far fault ones. Also the results show Hysteretic Energy caused by near fault records that are more than the far fault ones. What is more, as the building height rises, the share of building’s higher stories from the Hysteretic Energy increases. Keywords: Inelastic dynamic behavior, Energy concepts, Hysteretic Energy, Equalized near and far records, Nonlinear dynamic analysi

SEISMIC FRAGILITY ANALYSIS OF IMPROVED RC FRAMES USING DIFFERENT TYPES OF BRACING

Application of bracings to increase the lateral stiffness of building structures is a technique of seismic improvement that engineers frequently have recourse to. Accordingly, investigating the role of bracings in concrete structures along with the development of seismic fragility curves are of overriding concern to civil engineers. In this research, an ordinary RC building, designed according to the 1st edition of Iranian seismic code, was selected for examination. According to FEMA 356 code, this building is considered to be vulnerable. To improve the seismic performance of this building, 3 different types of bracings, which are Concentrically Braced Frames, Eccentrically Braced Frames and Buckling Restrained Frames were employed, and each bracing element was distributed in 3 different locations in the building. The researchers developed fragility curves and utilized 30 earthquake records on the Peak Ground Acceleration seismic intensity scale to carry out a time history analysis. Tow damage scale, including Inter-Story Drifts and Plastic Axial Deformation were also used. The numerical results obtained from this investigation confirm that Plastic Axial Deformation is more reliable than conventional approaches in developing fragility curves for retrofitted frames. In lieu of what is proposed, the researchers selected the suitable damage scale and developed and compared log-normal distribution of fragility curves first for the original and then for the retrofitted building

Modeling of fatigue life in double shear lap joints using artificial neural networks

Fatigue is one of the most important failure sources of material that is caused by repeatedly applied loads. It is a progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The experimental results of fatigue tests on Al-alloy 2024-T3 in double shear lap joints were used to estimate (model) fatigue life with artificial neural networks (ANN). Artificial neural networks with experimental data processing can find the knowledge or law lies behind the data, and unlike mathematical models, itâs not necessary to determine the mathematical relation between inputs and outputs. To model by artificial neural network, one of the experimental data of fatigue life randomly selected for validation and two other were selected for testing, the rest of the data were used to find the optimal values of weights and bias. After being ensured of the model accuracy, it was used to predict the fatigue life at different loads in the working phase that had not been tested. Comparison of experimental results and the results of the model shows that a 3-layer artificial neural network with less than 10% error could be used to predict the fatigue life at different loads

A Comparative Study of Bloom\'s Theory about Infection Control Methods Among Surgical Technologists and Students

Background & Aims of the Study: Nosocomial infection control has found a significant importance in prevention of mental stress, disabilities, declined life quality, mortality and shorter hospitalization as well as reducing the treatment costs. The aim of this study is to compare Bloom’s theory among operating room students and technologists about the infection control in 2014. Materials and Methods: This descriptive-analytical study was performed on 244 technologists and 113 students who were classified by random sampling. The data collection was carried out by a standardized two questionnaires: demographic data, and the knowledge, practice and attitudes about infection control questionnaire. Data analysis was conducted by SPSS V20 and Levene’s test, T-test, Chi-square and Kendall tau-b correlation coefficient were investigated. Results: The mean of knowledge and practice in terms of infection control were on medium level in both groups and they had positive attitudes. Based on T-test, the two groups showed no significant difference in knowledge and attitudes about infection control methods (p>0.05). The mean of practice was however significantly higher among technologists as compared with the students (P0.05). Based on Kendall tau-b correlation coefficient, the relationship between knowledge and practice was direct and significant. Conclusion: Regarding better practice of technologists, it is recommended to develop and establish clinical qualification tests on infection control for the students before their clinical practice. On the other hand, regarding the key role of technologists and students in prevention of nosocomial infections especially in operation rooms, enhancement of their knowledge and skills must be included in the educational and operational programs of authorities

Validity and reliability of the persian practice environment scale of nursing work index

Background: The practice environment pivotal role in patients and nurses better outcomes is evident. Practice Environment Scale of Nursing Work Index (PES-NWI) is widely utilized to assess nursing work environments. The present study was conducted to demonstrate the validity and reliability of the Persian version of PES-NWI. Materials and Methods: The instrument was translated and its psychometrics were investigated by content, construct validity (factor analysis), and homogeneity (internal consistency and intraclass correlation) on a sample of 350 nurses at educational hospitals in East Azerbaijan, Iran. Results: The 30 items loaded onto 4 factors explained 34.95–50.06% of the variance. The items across the factors differed slightly from those reported by the original author of the PES-NWI. Cronbach's alpha and Pearson coefficient for the entire instrument and also for extracted factors was 0.70–0.96. Conclusions: The Persian version of PES-NWI has an appropriate level of validity and reliability in the Iranian setting for nurses. The subscale of Nursing Foundations for quality care needs modification

Incorporation of natural lithium-ion trappers into graphene oxide nanosheets

Lithium consumption is estimated to face a considerable rise in the next decade; thus, finding new reproducible lithium resources such as brine deposits and seawater has become a fast-growing research topic. However, Li extraction from these resources is challenging due to its low concentration and presence of other monovalent cations exhibiting identical chemical properties. Here, it is discovered that tannic acid (TA) inside graphene oxide (GO) nanochannel acts as natural ion trapper, which possesses lithiophilic elements. The lithium-rich feed is achieved by using the potential-driven TA-GO membrane by excluding lithium ions from other monovalent cations. The results showed that the ion trapping capability of inexpensive TA-GO membrane is Li\ua0>\ua0Na\ua0>\ua0K with Li trapping energy of −593 KJ mol, respectively, where its trapping efficiency goes into a top rank among their expensive synthetic counterparts. Evaluating the combined effect of three key parameters, including barrier energy, hydration energy, and binding energy illustrates that required energy to transport Li-ion through the membrane is higher than that for other monovalent. This proof-of-concept work opens up an avenue of research for designing a new class of ion-selective membranes, based on the incorporation of naturally low cost available lithiophilic guest molecules into 2D membranes