Research On Layout Of Pharmaceutical Logistics Network Under Dynamic Demand

Under the background of the new medical reform,policies such as Internet Plus,One Vote System,Centralized Procurement,Medical Emergency Supplies Reserve,Carbon Peak and Carbon Neutrality have been implemented.It puts forward new requirements for the planning and construction of pharmaceutical logistics network.With the special situation of the evolution of COVID-19,the public’s habit of online consultation and drug purchase has been accelerated.In order to improve the efficiency of drug distribution and customer satisfaction,e-commerce enterprises have been cooperating with offline physical pharmacies.The dynamic needs of customers are meet by establishing pharmaceutical warehouse,accelerating the fusion of online and offline development.Because of the small batch and multi-frequency distribution of medical goods,higher requirements for inventory management are proposed.At the same time,the overall optimization of location and routing should be taken into account.Transportation and storage of medical items should be strictly limited to time and temperature.Cold chain transport and low temperature storage also contribute to an increase in carbon emissions.With the frequent occurrence of various public emergencies,it is easy to cause heavy casualties and property losses,which seriously endanger public security.In the face of sudden accidents,natural disasters,social security events and public health events,it is necessary to consider the development process of the event,road traffic conditions and the characteristics of the urgent demand for medical supplies.In order to support the scientific optimization of the medical emergency logistics network,the location of medical emergency logistics center and the allocation of medical materials should be considered.Therefore,the paper carries out research from the following three aspects.Firstly,aiming at the location planning and distribution route design of pharmaceutical pre-warehouse,a two-stage mathematical programming model of location-routing problem considering dynamic demand is established.The NSGA-III algorithm based on the reference point selection strategy is designed to solve the optimal solution set for the initial optimization stage,and the fuzzy clustering method is used to screen out the optimal scheme as the initial state of the dynamic optimization stage.Then NSGA-III algorithm is used during the dynamic optimization stage.Comparing with NSGA-II algorithm for time,Spacing,HRS and PR,it could be seen that NSGA-III runs faster,and gets more uniform solution set distribution and better convergence effect.And boxplots are drawn for further verification.The influence of the total fixed cost budget change of transportation vehicle type and pharmacy cooperative pre-warehouse on the three objective functions are calculated,and the sensitivity of the model and algorithm are tested.It indicates that third-party drug delivery enterprises are more suitable to use small and medium-sized vehicles to complete the delivery task and set appropriate location budget.Secondly,SPD model is proposed to solve the inventory fluctuation caused by the dynamic change of medical supplies.The influence of multiple modes of transportation on location layout,route planning and inventory strategy of regional pharmaceutical logistics center based on SPD model are considered.The total cost,total transportation time and total carbon emission of pharmaceutical logistics system are designed as objective functions,and a multi-objective optimization model of location-routing-inventory is established.NSGA-III algorithm is designed to solve the problem and compared with NSGA-II algorithm to analyze each indicator.NSGA-III algorithm maintains the balance between convergence and diversity and improves the efficiency of solving multi-objective problems.And boxplots are drawn for further verification.The sensitivity analysis of freight rates and stock safety factor is conducted,which verifies that the impact of them on cost,time and carbon emission should be fully considered when making decisions.Thirdly,according to the dynamic demand characteristics and road network characteristics of different medical supplies after the outbreak of public emergencies,the epidemic evolution is divided into four periods.Three scenarios are set up in each period,considering highway,railway and air transport modes.Three objective functions are established based on the transportation time,penalty cost and total cost of the medical emergency logistics system.And an optimization model of medical emergency logistics is proposed.The robust optimization method based on scenario strategy is used to transform the original model into a robust optimization model,and NSGA-III algorithm is used to solve the model.The comparative analysis of various performance indicators with NSGA-II algorithm is conducted.It is shown that although the running time of NSGA-III is longer in the first three periods,the operation time of NSGA-III is greatly reduced after entering the fourth period,and more Pareto optimal solutions could be solved.At the same time,NSGA-III solution set is more evenly distributed in each period,resulting in higher efficiency of Pareto optimal solution and better convergence effect.Boxplots are drawn for further verification.In order to analyze the robustness of the model,robust standard vectors and scenario probability are analyzed respectively,so that the decision makers of emergency rescue could formulate location-routing scheme according to their preferences for total time,penalty cost and total cost in different scenario stages.Based on the study of location and path of pharmaceutical pre-warehouse,it will help third-party drug distribution enterprises to take into account the cost factors,distribution efficiency and carbon emissions.By choosing the entity pharmacy with which to cooperate,the location decision and open location path optimization under complex circumstances are completed.The research on layout planning of regional pharmaceutical logistics network under SPD mode provides theoretical support for location-routing-inventory decision making,which is conducive to improving logistics management quality of enterprises and realizing effective cost control.The research on robust optimization of medical emergency logistics network will assist emergency logistics manager to design systematic and efficient multimodal transport scheme.It will improve the integrity,coordination and reliability of the emergency logistics network,enhance the self-recovery and anti-interference ability of the entire medical logistics emergency system.