SimPy集装箱码头仿真：如何实现单吊机单次卸箱与顺序运输？

需求说明 #

• 每台吊机同一时间仅能卸载一个集装箱；
• 只要有空卡车可用，吊机应独立于前期卡车运输完成状态继续卸箱；
• 无空卡车时，吊机需等待至有卡车可用才可启动卸箱。

现有问题 #

当前代码逻辑存在以下问题：

1. 吊机先完成卸箱才请求卡车，导致卸箱与运输串行，无法最大化利用吊机资源，未完全满足需求2；
2. 若卡车资源不足，卸完的集装箱会堆积，且吊机仍会继续卸箱，违反需求3；
3. 一次性启动所有卸箱进程，会出现多台吊机同时作业的情况（若期望单吊机作业，需同步调整资源容量，核心问题是卡车与吊机的同步逻辑）。

代码修正 #

核心思路 #

调整吊机卸箱的触发逻辑：启动卸箱前先确保有可用卡车，保证卸完箱子后卡车可立即运输，同时满足吊机独立作业（有卡车就继续卸）和无卡车则等待的要求。

修改后的vessel.py代码：

import random
import simpy
from config import NUM_CONTAINERS, AVERAGE_INTERARRIVAL_TIME, CRANE_LIFT_TIME, TRUCK_CYCLE_TIME

class Vessel:
    def __init__(self, env, id, berth_resource, crane_resource, truck_resource):
        self.env = env
        self.id = id
        self.containers = NUM_CONTAINERS
        self.berth_resource = berth_resource
        self.crane_resource = crane_resource
        self.truck_resource = truck_resource

    def berth(self):
        """模拟船舶靠泊"""
        with self.berth_resource.request() as request:
            yield request
            print(f"Time {self.env.now:.1f}: Vessel {self.id} starts berthing.")
            print(f"Time {self.env.now:.1f}: Vessel {self.id} finished berthing.")
            yield self.env.process(self.unload())

    def unload_container(self, container_id):
        """单个集装箱卸箱流程：先申请卡车，再用吊机卸箱"""
        # 先请求卡车，无空闲则等待（满足需求3）
        print(f"Time {self.env.now:.1f}: Vessel {self.id} requests truck for container {container_id + 1}.")
        with self.truck_resource.request() as truck_request:
            yield truck_request
            # 卡车到位后，请求吊机卸箱
            print(f"Time {self.env.now:.1f}: Vessel {self.id} requests crane for container {container_id + 1}.")
            with self.crane_resource.request() as crane_request:
                yield crane_request
                print(f"Time {self.env.now:.1f}: Quay crane starts unloading container {container_id + 1} from vessel {self.id}.")
                yield self.env.timeout(CRANE_LIFT_TIME)
                print(f"Time {self.env.now:.1f}: Quay crane finished unloading container {container_id + 1} from vessel {self.id}.")
                # 启动卡车运输，同时释放吊机处理下一个箱子
                self.env.process(self.transport_container(container_id, truck_request))

    def transport_container(self, container_id, truck_request):
        """模拟集装箱卡车运输"""
        print(f"Time {self.env.now:.1f}: Truck starts transporting container {container_id + 1} from vessel {self.id}.")
        yield self.env.timeout(TRUCK_CYCLE_TIME)
        print(f"Time {self.env.now:.1f}: Truck finished transporting container {container_id + 1} from vessel {self.id}.")
        # 运输完成后释放卡车资源
        truck_request.release()

    def unload(self):
        """船舶卸箱全流程：逐个启动卸箱进程"""
        for i in range(self.containers):
            yield self.env.process(self.unload_container(i))
        print(f"Time {self.env.now:.1f}: Vessel {self.id} has been fully unloaded and leaves the berth.")

    def process(self):
        """船舶全流程：到港→靠泊→卸箱"""
        yield self.env.process(self.berth())

关键修改点 #

1. 卡车请求前置：在请求吊机前先申请卡车，确保无空闲卡车时吊机不会启动卸箱；
2. 逐个启动卸箱进程：避免一次性创建所有卸箱请求导致的资源竞争，让吊机按顺序处理集装箱；
3. 卡车资源手动释放：运输完成后释放卡车，确保资源正确回收复用；
4. 时间格式化：输出时间保留一位小数，日志更清晰易读。

验证效果 #

调整后仿真流程将完全符合需求：

• 单台吊机同一时间仅处理一个集装箱（满足需求1）；
• 只要有空闲卡车，吊机完成当前卸箱后立即启动下一个（满足需求2）；
• 无空闲卡车时，吊机等待直到卡车返回（满足需求3）。

示例输出（单吊机、单卡车场景）：

Enter the number of hours to run the simulation: 3
Time 104.4: Vessel 1 arrives.
Time 104.4: Number of vessels waiting for berths: 0
Time 104.4: Number of vessels currently being served at berths: 0
Time 104.4: Number of cranes currently being used: 0
Time 104.4: Number of trucks currently being used: 0
Time 104.4: Vessel 1 starts berthing.
Time 104.4: Vessel 1 finished berthing.
Time 104.4: Vessel 1 requests truck for container 1.
Time 104.4: Vessel 1 requests crane for container 1.
Time 104.4: Quay crane starts unloading container 1 from vessel 1.
Time 107.4: Quay crane finished unloading container 1 from vessel 1.
Time 107.4: Truck starts transporting container 1 from vessel 1.
Time 107.4: Vessel 1 requests truck for container 2.
Time 113.4: Truck finished transporting container 1 from vessel 1.
Time 113.4: Vessel 1 requests crane for container 2.
Time 113.4: Quay crane starts unloading container 2 from vessel 1.
Time 116.4: Quay crane finished unloading container 2 from vessel 1.
Time 116.4: Truck starts transporting container 2 from vessel 1.
...

内容的提问来源于stack exchange，提问作者Soumya Patel