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Maintenance planning aims to improve the reliability of assets, prevent the occurrence of asset failures, and reduce maintenance costs associated with downtime of assets and maintenance resources (such as spare parts and workforce). Thus, effective maintenance planning is instrumental in ensuring high asset availability with the minimum cost. Nevertheless, to find such optimal planning is a nontrivial task due to the (i) complex and usually nonlinear inter-relationship between different planning decisions (e.g., inventory level and workforce capacity), and (ii) stochastic nature of the system (e.g., random failures of parts installed in assets). To alleviate these challenges, we study a joint maintenance planning problem by considering several decisions simultaneously, including workforce planning, workforce training, and spare parts inventory management. We develop a hybrid solution algorithm ($$\mathcal {DRLSA}$$ DRLSA ) that is a combination of Double Deep Q-Network based Deep Reinforcement Learning (DRL) and Simulated Annealing (SA) algorithms. In each episode of the proposed algorithm, the best solution found by DRL is delivered to SA to be used as an initial solution, and the best solution of SA is delivered to DRL to be used as the initial state. Different from the traditional SA algorithms where neighborhood structures are selected only randomly, the DRL part of $$\mathcal {DRLSA}$$ DRLSA learns to choose the best neighborhood structure to use based on experience gained from previous episodes. We compare the performance of the proposed solution algorithm with several well-known meta-heuristic algorithms, including Simulated Annealing, Genetic Algorithm (GA), and Variable Neighborhood Search (VNS). Further, we also develop a Machine Learning (ML) algorithm (i.e., K-Median) as another benchmark in which different properties of spare parts (e.g., failure rates, holding costs, and repair rates) are used as clustering features for the ML algorithm. Our study reveals that the $$\mathcal {DRLSA}$$ DRLSA finds the optimal solutions for relatively small-size instances, and it has the potential to outperform traditional meta-heuristic and ML algorithms.

The predictability of wind energy is crucial due to the uncertain and intermittent features of wind energy. This study proposes wind speed forecasting models, which employ time series clustering approaches and deep learning methods. The deep learning (LSTM) model utilizes the preprocessed data as input and returns data features. The Dirichlet mixture model and dynamic time-warping method cluster the time-series data features and then deep learning in forecasting. Particularly, the Dirichlet mixture model and dynamic warping method cluster the time-series data features. Next, the deep learning models use the entire (global) and clustered (local) data to capture the long-term and short-term patterns, respectively. Furthermore, an ensemble model is obtained by integrating the global model and local model results to exploit the advantages of both models. Our models are tested on four different wind data obtained from locations in Turkey with different wind regimes and geographical aspects. The numerical results indicate that the proposed ensemble models achieve the best accuracy compared to the deep learning method (LSTM). The results imply that the feature clustering approach accommodates a promising framework in forecasting.

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