Estimation of component redundancy in optimal age maintenance

The classical Optimal Age-Replacement defines the maintenance strategy based on the equipment failure consequences. For severe consequences an early equipment replacement is recommended. For minor consequences the repair after failure is proposed. One way of reducing the failure consequences is the use of redundancies, especially if the equipment failure rate is decreasing over time, since in this case the preventive replacement does not reduce the risk of failure. The estimation of an active component redundancy degree is very important in order to minimize the life-cycle cost. If it is possible to make these estimations in the early phase of system design, the implementation is easier and the amortization faster. This work proposes an adaptation of the Optimal Age-Replacement method in order to simultaneously optimize the equipment redundancy allocation and the maintenance plan. The main goal is to provide a simple methodology, requiring the fewer data possible. A set of examples are presented illustrating that this methodology covers a wide variety of operating conditions. The optimization of the number of repairs between each replacement, in the cases of imperfect repairs, is another feature of this methodology

Component redundancy allocation in optimal cost preventive maintenance scheduling

This work presents a methodology to assist maintenance teams in defining the maintenance schedule and redundancy allocation that minimise the life-cycle average cost of a system. The minimal data required are three average costs and one reliability function. This methodology is useful in a system design phase, since in this situation data is usually scarce or inaccurate, but can also be applied in the exploration phase. It consists of an adaptation of the classical optimal age replacement method, combined with a redundancy allocation problem. A set of simple illustrative examples covering a variety of operating conditions is presented, demonstrating quantitatively the applicability of the methodology to a range of maintenance optimisation decisions

Flower strips and remnant semi‐natural vegetation have different impacts on pollination and productivity of sunflower crops

1. Intensification of agricultural landscapes to fulfil increased global food de-mands has dramatically impacted biodiversity and ecosystem services. Several pollinator groups, which are vital for the maintenance of pollinator-dependent crops, have been severely affected by this intensification pro-cess. Management tools, such as the implementation of agri-environmental schemes, have been widely proposed to improve pollinator's communities and pollination services, although the effectiveness of wildflower strips in com-parison to existing natural or semi- natural habitats and the impact on yield has not been fully demonstrated. 2. Here, we aimed to assess the effect of flower strips implementation near sun-flower fields in two intensive agricultural regions and to quantify their impact on visitation rates and sunflower productivity. Data were obtained in two regions in Spain (Burgos and Cuenca) in sunflower fields with associated semi- natural veg-etation (SNVs), with implemented wildflower strips (WFSs) and without vegeta-tion structures (NonVs). Visitation rates were monitored over 2 years by direct observations, and both sunflower seed production and weight were assessed in 52 fields per year. 3. Our results revealed regional and inter-annual variation in visitation rates, likely driven by structural differences in the landscapes studied. In Cuenca, character-ized by more heterogeneous and floral resources- richer landscapes, the effects of WFSs were significant in the second year of implementation, with higher visi-tation rates and productivity values in fields with implemented wildflower strips compared to those without. In contrast, in Burgos, no consistent effects among field treatments between years were observed. 4. Synthesis and applications. The implementation of flower strips or maintenance of remnant semi- natural habitats adjacent to sunflower fields showed context- dependent effects on pollinator visitation rates and crop yield. In highly sim-plified agroecosystems, these interventions may be insufficient or may need longer times to produce significant effects. Yet, in regions where natural and semi-natural patches were already present, the implementation of flower strips was a successful strategy to promote pollinators and sunflower productivity