Study On Vehicle Routing Problem Of Two-Echelon Cold Chain Logistics Network Under Carbon Cap-and-Trade Mechanism

With the rapid development of national economy and continuous improvement of national income levels,people's demand for cold chain products such as fresh products are increasing,and the domestic cold chain logistics industry has ushered in a golden development period.Facing such huge demand of market,China's cold chain logistics industry,which is still in its infancy,has lots of problems need to be solved,such as high decay rate of products,serious environmental pollution,and low punctuality rate of delivery time.High cost of product corruption lower the profit of cold chain logistics companies and become a key issue which hindering the development of cold chain logistics industry;environmental pollution caused by high energy consumption prompt relevant government agencies to strengthen the supervision of carbon emissions in cold chain logistics industry;lacking of scientific and reasonable distribution plans prevents the timely delivery of goods and causes the loss of loyal customers.Therefore,based on the research on the vehicle routing problem of the existing cold chain logistics network and the implementation background of the carbon quota trading policy,this paper launches a complex two-echelon cold chain logistics network with considerations of economic requirements,environmental protection requirements and customer satisfaction requirements for third-party logistics carriers,which has a guiding significance to help cold chain logistics enterprises to balance the profit and environmental impact,improve industry competitiveness and help the government to supervise and regulate the carbon emission market.The main research results of this paper are as follows:Firstly,the proposed vehicle routing problem for two-echelon cold chain logistics network under the carbon cap-and-trade mechanism expands the traditional single-level logistics network vehicle routing problem to a two-level logistics network-based vehicle routing problem.The modeling process is not limited to a certain optimization objective such as economic costs or environmental pollution,but to construct a multi-objective optimization model of vehicle routing problem which is closer to the actual application scenario of cold chain logistics.Besides,the model focuses on the economic costs such as fixed costs caused by vehicle operation and maintenance and driver salaries,the deterioration costs of cold-chain goods,and the energy consumption costs caused by equipment operation,model use the carbon cap-and trade mechanism monetize the carbon dioxide emissions generated by energy consumption to carbon emission costs,and the membership function of fuzzy time window is also used to measure the customer satisfaction corresponding to delivery time.Secondly,considering the objective function of customer satisfaction based on fuzzy time window increases the difficulty of solving optimization model,this paper applied a method named ?-restriction to convert the objective function of overall customer satisfaction into satisfaction constraints,and finally obtains a single optimization model of vehicle routing problem for two-echelon cold chain logistics network under the carbon cap-and-trade mechanism that is used to solve the optimal vehicle distribution plan with the lowest total costs and a certain level of overall customer satisfaction.At the same time,this paper designed a set of improved adaptive genetic algorithm including elite selection strategy,adaptive cross probability and mutation probability adjustment mechanism to solve the optimization model,and then valid the performance of algorithm by standard data set examples.Finally,taking a Shenzhen cold chain logistics enterprise's vehicle path decision problem as an example,using the proposed optimization model to obtain optimal vehicle routes plans under different overall customer satisfaction constraints or different parameter settings of the carbon cap-and trade mechanism.By comparing and analyzing the results of plans,we can find that the selection of the lower limit of overall customer satisfaction is particularly important for optimization effects of optimization model.Once the lower limit of overall customer satisfaction exceeds a certain threshold,the total cost and carbon emissions of optimal vehicle route will rise sharply;and the value of unit carbon price and carbon quota in the carbon cap-and-trade mechanism also affects the output of the model.Carbon price with lower value cannot urge enterprises to control their emissions,however,high value of carbon price setting also bring greater economic pressure on companies.Therefore,it is wise for government to set appropriate carbon price values and carbon quotas that are close to the actual carbon emissions data of companies during the formulating period of carbon cap-and trade policies to achieve better emission reduction effects.