As an important over-current component of the waterjet propulsion system, the main function of a nozzle is to transform the mechanical energy of the propulsion pump into the kinetic energy of the water and eject the water flow to obtain thrust. In this study, the nozzle with different geometry and parameters was simulated based on computational fluid dynamics simulation and experiment. Numerical results show a good agreement with experimental results. The results show that the nozzle with a circular shape outlet shrinks evenly. Under the designed flow rate condition, the velocity uniformity of the circular nozzle is 0.26% and 0.34% higher than that of the elliptical nozzle and the rounded rectangle nozzle, respectively. The pump efficiency of the circular nozzle is 0.31% and 0.14% higher than that of the others. The pressure recovery and hydraulic loss of the circular nozzle are superior. The hydraulic characteristics of the propulsion pump and waterjet propulsion system are optimal when the nozzle area is 30% times the outlet area of the inlet duct. Thus, the shaft power, head, thrust, and system efficiency of the propulsion pump and waterjet propulsion system are maximized. The system efficiency curve decreases rapidly when the outlet area exceeds 30% times the outlet area of the inlet duct. The transition curve forms greatly affect thrust and system efficiency. The transition of the linear contraction shows improved uniformity, and the hydraulic loss is reduced. Furthermore, the hydraulic performance of the nozzle with a linear contraction transition is better than that of others.

The waterjet propulsion system has been widely used in the military and civil fields because of its advantages of in terms of high efficiency and energy savings. In order to study the three-dimensional cavitation flow in the waterjet propulsion pump, the cavitation process of the waterjet propulsion pump was simulated numerically using the Zwart–Gerber–Belamri cavitation model and the RNG (Renormalization Group) k-ε model. The simulation results of cavitation on the waterjet propulsion pump and pump system show that, in the initial stage of cavitation, vapors first collect on the leading edge of the suction surface of the blade near the rim of the impeller. As the total pressure at the impeller inlet decreases, the cavitation region expands toward the trailing edge and the vapor fraction volume gradually increases. In order to simulate the cavitation state of the waterjet propulsion pump under the actual working conditions, a numerical simulation of the entire waterjet propulsion pump system with inlet passage was carried out. After assembling the inlet passage, the flow pattern at the impeller inlet becomes uneven, leading to irregular changes in the cavitation region of the impeller. The potential danger regions of cavitation are the lip of inlet passage and the upper and lower connecting curved section of the inlet passage. The performance of waterjet propulsion pump system changes greatly when the net positive suction head available (NPSHa) value of the pump reaches the critical value.

The quality of agri-foods in e-supply chains confronts more threats than that in the traditional agri-food supply chain. However, most of the existing studies focusing on the quality problems of fresh agri-products are mainly cases studies and statistical analyses, and they do not take into account the farmers’ willingness to comply with safe agri-food supply procedures. To solve the supply quality problems of fresh agri-foods and help participators make a better choice, the decision-making behavior on the supply quality of agri-foods in the e-supply chain was deeply studied in this paper using game theory. Some factors related to the decision behavior of the supply chain were analyzed, including the supervision intension of the government, the rights protection consciousness of consumers, and the intensity of punishment for poor-quality agri-foods. These factors have an important influence on the farmers’ willingness to provide high-quality products and e-business’ probability of inspection. Compared with three different decision models of agri-food e-supply chains, the results show that the decentralized decision model is better than the centralized model from the view of quality protection. The behavior of members of the supply chain is as follows: the farmers’ willingness to supply high-quality agri-foods increases with the increase in the consumers’ consciousness of their rights and the government’s supervision intensity. The “experience deviation” phenomenon also occurs when a new e-business makes a decision about its quality inspection behavior in this e-supply chain where the quality information is traceable. As such, e-business enterprises should reduce their quality inspection behavior based on the increase in the government’s supervision intensity. This happens to be opposite to the traditional experience where quality information is not traceable. This study not only extends the research framework of the novel electronic supply chain, but also provides a certain reference for the subsequent research and e-business practices of fresh produce in developing countries.

Based on the realistic concerns about the improvement of the quality of agricultural foods (agri-foods), the optimal supply quality and price subsidy strategies of producers and sellers for the two-level agricultural supply chain, composed of a producer and a seller, are studied. The differences in the quality safety, price, and market demand of agri-foods in the supply chain are compared and analyzed. The study found that the maximum profit of supply chain participants decreases with the increase of price elasticity of demand. When the quality of agri-foods is upgraded in a producer-led manner, the quality of agri-foods in the supply chain does not undergo substantial improvement, and the maximum profit of agri-foods operators is insensitive to the price elasticity of demand at this time. When the seller-led quality upgrading is launched, the maximum profit of the producer decreases with the increase of the quality elasticity of demand, the maximum profit of the seller increases with the increase of the quality elasticity of demand, and the total profit of the supply chain also increases with the increase of the quality elasticity of demand under the centralized decision situation. The quality and safety of agri-foods as well as the overall profit of the supply chain can be improved most effectively under the centralized control decision with the goal of maximizing the supply chain benefits. In terms of quality and price, quality improvement actions of agri-foods driven by supply-side producers are less effective than those driven by demand-side consumption. In addition, cost-sharing contracts can significantly improve the quality of agri-foods in the supply chain and make them more “high-quality and low-price” than before the adoption of cost-sharing contracts.

This study undertakes a comprehensive analysis of vegetable production efficiency in China using input–output data from 30 provinces spanning 2011 to 2017. By incorporating environmental pollution costs as undesirable outputs alongside vegetable output value, we employ Data Envelopment Analysis (DEA) with the Banker, Charnes, and Cooper (BCC) model and the Malmquist index model. Our assessment reveals both annual and inter-period efficiency changes. The findings highlight a modest overall efficiency in China’s vegetable production and significant regional disparities. Technical progress emerges as a pivotal determinant of total factor productivity (TFP). Recognizing these dynamics, we propose policy recommendations that prioritize technical innovation, sustainable practices, rural infrastructure enhancement, and specialized cultivation methods. Implementing these recommendations could bolster China’s position in international trade negotiations due to increased exports and potentially drive broader environmental policy reforms. As vegetable production becomes more efficient and sustainable, there might be a shift in labor needs, potentially leading to migration patterns or changes in employment structures. These insights contribute to the sustainable development of China’s vegetable industry, offering a broader understanding of the dynamics of agricultural efficiency in the context of environmental sustainability.

The purchasing decisions of consumers increasingly incorporate considerations of freshness and the carbon footprint of agri-foods. This study aims to investigate the impact of consumer preferences on decision-making behavior within dual-channel supply chains. Specifically, it classifies the structure of the supply chain channels into two types: producer-led and seller-led online channels, and examines two distinct decision-making scenarios: centralized and decentralized decision-making. The study applies the game theory modeling method to analyze the differences in the selling prices, freshness, low carbon levels, and profits of agri-foods in these scenarios. The findings indicate that as consumer preference for the online channel grows, it becomes more challenging to sell homogeneous agri-foods at higher prices through physical (entity) channels. Moreover, the introduction of online channels by sellers leads to higher selling prices for agri-foods in the supply chain under decentralized decision-making compared to centralized decision-making, and the freshness and low carbon level of agri-foods primarily depend on the cost structure of the supply chain. From the perspective of enhancing produce quality, promoting low carbon development, and attaining high-quality products at a reasonable price, centralized decision-making within the supply chain and seller-led online channels are more advantageous. However, it is important to note that pursuing these benefits may result in a certain amount of sacrifice in terms of supply chain profit.