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This study proposes a genetic algorithm to solve the biobjective vehicle routing problem with time windows simultaneously considering total distance and distance balance of active vehicle fleet. A new complex chromosome is used to present the active vehicle route. Through tournament selection, one-point crossover, and migrating mutation operator, the solution of the problem is solved. In experiment on Solomon's benchmark problems, considering the total distance and distance balance, the results are improved in all classes of problems. According to the experimental results, the suggested approach is sufficient and the average GA performance is good.

Based on the work breakdown structure theory, the lean shipbuilding method guided by intermediate products is proposed in this article. The hull segment task package is divided according to the content of the shipbuilding operation. Considering the constraints of resources and personnel at the production site, the scheduling strategy of the task package is formulated. Moreover, a virtual flow production system of the shipbuilding workshop is established. On this basis, a lean shipbuilding manufacturing execution system for small and medium-sized shipbuilding enterprises is developed to achieve lean production in a shipbuilding workshop. The application results indicate that implementation of the lean shipbuilding method and manufacturing execution system can significantly reduce the ship production cycle and the number of operators, as well as improve the production efficiency. Introduction In recent years, to resist strong international competition, manufacturers are under great pressure to develop products more efficiently and economically (Nam et al. 2016). The ship manufacturing industry, which faces fierce market competition, helps many nations’ economic systems (Rahman & Karim 2015). For example, the shipbuilding industry contributed over $37 billion of the Gross Domestic Product (GDP) to the U.S. economy in 2013 (MARAD 2015). Currently, China’s shipbuilding industry is in a downturn. If the shipbuilding enterprises want to survive and improve their competitiveness, they must reduce labor costs and shorten the production cycle. Lean production is a type of management philosophy born in Toyota Motors. One of the lean thinking goals is to eliminate waste, which can increase work satisfaction and turn waste into value. It should be emphasized that lean thinking must go beyond the company. In other words, lean thinking has to be employed from the product design to the set of activities delivered to the end customer (Barbosa 2014). Lean manufacturing technology focuses on eliminating all types of waste in the manufacturing process and reducing the lead time (Zhu et al. 2019).

With continuous improvements in the function and performance of ship equipment, mechanisms of failure have become more and more complicated. To avoid over-maintenance or under-maintenance in existing routine ship maintenance strategies, a ship-level method for repair decisions based on the preventive maintenance concept is proposed in this paper. First, the anticipated repair demand levels of key components are calculated using an improved failure mode and effects analysis (FMEA) method; second, a Weibull distribution model is established, and the parameters are estimated using the maximum likelihood estimation (MLE) to predict the characteristic life of the equipment; then, logical decision principles and rule-based reasoning (RBR) are used to determine the ship repair level and repair timing. Finally, the feasibility and application value of the proposed repair strategy were verified by case studies, and a ship-level system for repair decisions was established.

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