Estimating maintenance costs of a wind turbine pitch control system

Wind turbines are nowadays the principal source of wind energy production. However, the technical information publicly known about these machines is still very scarce. Indeed, information related to failure modes, unavailability and maintenance costs of these systems remains confidential and only is held by manufacturers. To be able to optimize the efficiency, to guarantee the security and to negotiate better warranty and maintenance contracts, it is necessary to know more information about the operation and maintenance and replacement costs of subsystems of a wind turbine. To this end, this paper presents a short literature review of what has been published so far about this issue, and, based on two years of operation, analyses an active power control system of 21 identical wind turbines, installed in a wind farm in Portugal. The emphasis of this study is on the operation, availability and maintenance, and replacement costs of the active pitch control device, which automatically manages the position and operation of blades according to wind direction and speed, thus maximizing the electrical power gathered from the natural forces. Moreover, the paper provides an estimation for the total maintenance cost of this device, one of the most important components of the wind turbine, thus allowing wind farm companies to carry out financial and economic analysis of maintenance contracts that probably will be the rationale for better contract negotiations with manufactures. The result and the analyses that have been reported may also contribute for further studies on the reliability and maintenance policies of wind turbines.This work was financed with FEDER Funds by Programa Operacional Fatores de Competitividade – COMPETE and by National Funds by FCT – Fundação para a Ciência e Tecnologia, Project: FCOMP-01-0124-FEDER-022674.info:eu-repo/semantics/publishedVersio

A hybrid bi-objective optimization approach for joint determination of safety stock and safety time buffers in multi-item single-stage industrial supply chains

In material requirements planning (MRP) systems, safety stock and safety time are two well-known inventory buffering strategies to protect against supply and demand uncertainties. While the role of safety stocks in coping with uncertainty is well studied, safety time has received only scarce attention in the supply chain management literature. Particularly, most previous operations research models have typically considered the use of such inventory buffers in a separate fashion, but not together. Here, we propose a decision support system (DSS) to address the problem of integrating optimal safety stock and safety time decisions at the component level, in multi-supplier multi-item single-stage industrial supply chains under dynamic demands and stochastic lead times. The DSS is based on a hybrid bi-objective optimization approach that simultaneously optimizes upstream inventory holding costs and β-service levels, suggesting multiple non-dominated Pareto-optimal solutions to decision-makers. We further explore a weighted closed-form analytical expression to select a single Pareto-optimal point from a set of non-dominated solutions, thereby enhancing the practical application of the proposed DSS. We describe the implementation of our approach in a major automotive electronics company operating under a myriad of components with dynamic demand, uncertain supply and requirements plans with different degrees of sparsity. We show the potential of our approach to improve β-service levels while minimizing inventory-related costs. The results suggest that, in certain cases, it appears to be more cost-effective to combine safety stock with safety time compared to considering each inventory buffer independently.This work has been supported by the European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Internationalization Pro-gram (COMPETE 2020) [Project No. 39479, Funding reference: POCI-01–0247-FEDER-39479]

Anticorpos anti-VIH1 e VIH2 em doentes com Tuberculose. Experiência de um trabalho realizado ao longo de 3 anos nas regiões de Lisboa, Barreiro e Santarém

ABSTRACTSettingPatients with active tuberculosis.ObjectiveTo evaluate the rates of anti-HIV1 and anti-HIV2 antibodies in patients with active Tuberculosis.DesignAnti-HIV antibodies, were searched by ELISA and confirmed by Western blot.ResultsWe studied 767 patients (479 men and 288 women); 671 of them were caucasian, 76 black and 20 from other races. Eighteen of them were intravenous-drug users (IVDU), 35 had been transfused, 630 were heterosexual and in 121 we didn’t obtain data about sexual behaviour; 153 sojourned in Africa for different periods of time; 541 patients (70.5%) had pulmonary tuberculosis, 164 (21.4%) had extrapulmonary tuberculosis, 44 (5,7%) patients presented pulmonary and extrapulmonary tuberculosis and 18 (2.3%) had primary tuberculosis. Fourteen (1.8%) patients bad anti-HIV antibodies: 10 HIV1 and 4 HIV2; all seropositive were heterosexual, one being IVDU; 5 had pulmonary tuberculosis and 9 had extra-pulmonary tuberculosis (including all 4 cases with HIV2).ConclusionsWe found a rate in our population of 1.8% particularly in black patients (3.9%); serum positivity was more frequent in patients with extrapulmonary tuberculosis particularly in HIV2 patients. We advise for systematic screening