It can divide high-density areas into clusters, and can also divide clusters of different shapes in noisy data.
Compared with the K-MEANS clustering method, there is no need to input the number of clusters to be divided in advance.
You can input parameters to filter noise when needed.
After clustering, the material demand customers are divided into different groups and individual discrete customers, and each discrete customer is treated as a separate category. At the same time, the closest vehicle delivery customer point to the clustered customer is identified as the density corresponding customer, which is used as the location for the launch and recovery of the vehicle mounted UAV.
4.1.2. Dual Objective Processing in the Model
The model constructed in this article includes two objectives: (1) the shortest total delivery time and (2) the highest customer satisfaction. Based on the high complexity of the dual objective function in the optimization process, the dual objective function model is transformed into a single objective function optimization model for solution. Given that the approach and operation of adding penalty factors are both easy, this method is adopted in the article to handle the dual objectives in the model. The specific processing steps are as follows: Step 1: Since the highest customer satisfaction is a maximum problem, directly adding a penalty factor will not match the total delivery time of the minimum problem and does not conform to logical reasoning. Therefore, taking a negative customer satisfaction value and adding a time penalty factor will result. Then add it linearly to the total delivery time.
Step 2: Taking a negative value for customer satisfaction may lead to an imbalance between the two objective functions, resulting in a negative total objective function value. Therefore, it is necessary to select an appropriate time penalty factor . In the text, the average satisfaction value is set at 0.5. When the satisfaction is greater than take 0.25; When satisfaction is less than take 0.75. Make both objectives achieve good results in optimization. However, the optimization direction of the dual objective function is different, and the optimization of objective F1 will inevitably affect the optimization of objective F2. In the end, a satisfactory solution can only be obtained according to actual requirements.
The final optimization objective function after processing is:
(Where F is the transformed objective function)
The rate of return is positively correlated with the probability of selecting a food source, so the probability of bees being recruited to which food source is also positively correlated with the rate of return on the food source 55,56]. The process of artificial bee colony algorithm is shown in
Figure 5.
The ABC algorithm has the characteristics of fewer parameters, simplicity, and easy implementation. In the past decade, ABC has been successfully applied to solve TSP problems, and its powerful optimization capabilities and outstanding search advantages in TSP and VRP have been tested. TSP-MD is an extension of TSP, and the close relationship between TSP and TSP-MD lays the foundation for handling TSP-MD.
4.1.3. Artificial Bee Colony Algorithm Initialization and Neighborhood Search Strategy
The UAV Road section is the path generated by dividing the number of UAVs into individual units in a group. The optimal solution of the vehicle and the optimal solution of the UAV are combined using cross chain coding to form a joint delivery path, as shown in
Figure 6:
When the artificial bee colony algorithm executes a process, initialization is the first crucial step, which includes the population size
, the number of iterations required, and the maximum search limit. The initial solution is generated through a random method, which is the path sequence
from the starting warehouse to the visiting customer and then back to the warehouse. SN is the number of food sources that need to be delivered to the customer. In the search process, neighborhood search strategies are divided into three methods: exchange, insertion, and reverse order, as shown in
Figure 7.
4.1.4 Decoding Strategy for UAV Path
The initial solution is constructed using a UAV insertion path strategy. If
UAVs simultaneously deliver
customers, the decoding diagram of element
in the obtained solution is shown in
Figure 8:
4.1.5. Adaptive Probability Design for Following Bees
This section describes the design of adaptive probability for following bees in artificial bee colony algorithms. The common feature of heuristic algorithms is that they are selected according to a certain probability, and how the selected probability is allocated has a significant impact on the optimization efficiency of the algorithm. Optimizing randomness is one of the characteristics of artificial bee colony algorithms, and the follower bees in the algorithm heavily rely on probability to choose when searching for the optimal process. In the ABC algorithm, the follower bee adopts a roulette wheel method to select the leader bee. Its characteristic is that as the fitness value increases, the probability of being selected increases, which is the basic probability selection, as shown in
Figure 9. This method will make bees quickly gather towards food sources with high nectar value, making it difficult to ensure the diversity of food sources. To some extent, it will abandon many potential high-value food sources and prematurely fall into local optima. In order to improve the optimization effect of the algorithm and increase the diversity of food sources, an adaptive probability selection strategy is proposed. The strategy based on adaptive probability is based on the fitness probability of the population, and the selection probability is allocated according to changes in the number of iterations, in order to achieve the goal of selecting the probability of food sources even when the fitness value is small, as shown in
Figure 10. The design of the adaptive process requires calculating the fitness probability of the food source, and the probability of the food source being selected is calculated by formula 4.1:
Among them, is the probability of food source fitness, and is the number of iterations.
By comparing the results of basic probability selection in
Figure 9 with the adaptive probability selection in
Figure 10, it can be seen that the adaptive probability can exhibit a parabolic shape, allowing for a high chance of being selected even when the initial fitness value is small. This not only improves the probability of food sources being selected when the initial fitness value is small before improvement, but also takes into account the probability of being selected when the fitness value is large, achieving the goal of diverse populations.
Based on the above design process, the detailed steps for solving the model using artificial bee colony algorithm are obtained:
Order 1: reads the coordinate point information of the delivery demand customer. The first allocation is the collection of demand customers who can receive delivery services from vehicles and cannot receive delivery from vehicles after departing from the distribution center. The number of demand customers is n, code each material demand customer, and then obtain the expected delivery time, demand, and vehicle and UAV load characteristics of each material demand customer.
Order 2: calculates the distance between each customer and forms a distance matrix.
Order 3: This includes: population size, number of leading bees, number of following bees, maximum number of leading bee searches, number of reconnaissance bees, number of iterations, number of customers, and number of UAVs.
Order 4: initializes the population based on the method used in the algorithm design to generate initial solutions, and calculates the fitness values of each solution based on the objective function and fitness function.
Order 5: runs the algorithm and begins the iteration process, repeating Order 6 to Order 12.
Order 6: leads the bee phase to execute all solutions once and continue searching for new solutions within the neighborhood of the solutions. And update the solution with a higher fitness value than the original solution based on the principle of greed.
Order 7: If the state of the solution in Order 7 has not been updated, the number of local searches corresponding to the solution is limited to limit+1. If the solution is updated, the corresponding search frequency variable limit=0.
Order 8: obtains the basic fitness probability based on the fitness values of all solutions, and then calculates the adaptive probability values of each solution being selected by the following bee.
Order 9: follows the bee to select all solutions according to the selected probability value calculated in Order 8. It continues to search for new solutions locally near the current solution, evaluates the fitness of the found new solutions, and still follows the greedy principle of selecting the optimal solution from the new solutions while saving the original solution. If the current solution has not been updated, the local search frequency variable corresponding to the current solution is also limited = limit + 1. If the solution is updated, limit = 0.
Order 10: If there is no updated solution within the Limit, discard the solution and switch to the reconnaissance bee stage to find a regenerated solution to replace it.
Order 11: records the current optimal solution.
Order 12: determines whether the global maximum cycle of iterations has been reached. If it has, it indicates the end of the algorithm. Otherwise, it goes to Order 6 and Order 11, where the recorded solution is the global optimal solution.