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Aniket Hingane
Aniket Hingane

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Optimizing Maritime Port Congestion with Dependency-Driven Multi-Agent Simulation

How I Built an Agentic Berth Allocator and Queue Scheduler to Minimize Vessel Demurrage Costs

Optimizing Maritime Port Congestion with Dependency-Driven Multi-Agent Simulation

How I Built an Agentic Berth Allocator and Queue Scheduler to Minimize Vessel Demurrage Costs

Title Animation

TL;DR

This article document is a write-up of a personal experiment I ran to address a major bottleneck in global trade: maritime port congestion and vessel scheduling. In my observation, ports traditionally rely on rigid, linear First-Come-First-Served (FCFS) dispatch logic which fails to account for dynamic demurrage penalties or physical vessel constraints. To study this problem, I built a modular Python simulation engine named AnchorFlow-AI. The system implements a dependency-driven multi-agent dispatch optimizer where specialized agents coordinate to schedule berthing transits and manage shared resources (tugs and pilots). Under simulated weather disruptions and equipment failures, my agentic coordination framework yielded a 16.4% reduction in vessel waiting times and saved over $480,000 USD in demurrage penalties compared to the FCFS baseline. The codebase is publicly available on GitHub for verification.

Introduction

Global supply chains hinge on the efficiency of maritime ports, yet port operations remain vulnerable to severe delays. From my experience observing logistics operations, the scheduling of container ships, dry bulk carriers, and Suezmax tankers is still frequently managed using static spreadsheets or basic scheduling rules. When a port channel closes due to heavy fog or a berth crane experiences mechanical failure, the port operations scheduler faces a combinatorial nightmare. Re-routing incoming ships, re-allocating crane crews, and rescheduling harbor pilots or tugboats requires dynamic, multi-factor trade-offs.

I wrote this article because I wanted to investigate whether a Prompt-Agent-Skill framework could solve this coordination challenge. In my opinion, the highest leverage use of intelligent systems in logistics is not simple automated planning, but active delivery orchestration. I wanted to design a simulation where vessel agents, berth allocation agents, and resource transit agents cooperate in real-time to solve a multi-billion-dollar business problem.

To keep this study rigorous and transparent, I built a self-contained Python simulator that runs on a single laptop. I avoided external cloud dependencies or hosted databases, choosing instead to write pure Python modules using NumPy and Matplotlib for data processing. This experimental write-up details the mathematical and structural design decisions I made, walks through the codebase section-by-section, and compares the outcomes of the agentic optimizer against traditional scheduling policies.

Title Flowchart

What's This Article About?

  1. This article details the design and implementation of AnchorFlow-AI, an agentic maritime simulation platform built to mitigate port congestion and demurrage costs.
  2. I explain how I translated the Prompt-Agent-Skill design pattern into a functional multi-agent coordination loop for logistics orchestration.
  3. I describe the mathematical triage weight formula I designed to evaluate anchorage queues dynamically based on demurrage accumulation rates.
  4. I walk through the complete source code, illustrating how individual skills are governed, validated, and executed within the port environment.
  5. I present a comparative data analysis of FCFS vs. Agentic scheduling runs under identical weather and mechanical disruption sequences.

Tech Stack

  1. Python 3.12: The core programming language used to implement the simulator, agent logic, and execution CLI.
  2. NumPy & Pandas: Utilized for statistical event generation, data manipulation, and calculating metrics.
  3. Matplotlib: Used to compile simulation logs and output the comparative performance charts.
  4. Rich: Integrated to format and render the detailed ASCII metrics table in the command line interface.

Why Read It?

  1. If you are exploring how to apply agentic design patterns to operational research, this PoC provides a concrete, multi-agent framework for resource allocation.
  2. If you want to understand the limits of linear queuing models in logistics, the comparative data charts offer a clear visualization of delay propagation.
  3. If you value reproducibility, the entire project is structured to run locally with a static seed, allowing you to run the simulation yourself and verify the results.
  4. From my perspective, this article serves as an honest look at the trade-offs involved in dynamic scheduling, showing exactly where heuristic models fail and agentic models succeed.

Let's Design

Port Physical & Resource Topology

In my view, modeling port congestion requires a high-fidelity representation of the physical infrastructure and shared transit resources. I structured the port topology around three distinct entities: anchorage waiting areas, berths, and harbor transit resources.

  1. Anchorage Queue: A designated offshore waiting area where vessels drop anchor upon arrival. While a vessel remains in the anchorage queue, it accumulates demurrage costs according to its charterparty agreement.
  2. Berths: Dedicated dock spaces where cargo operations occur. Each berth has distinct physical specifications, including Maximum Length Over All (LOA) and Maximum Draft Depth. A Suezmax tanker drawing 14 meters of water cannot dock at a feeder container berth with a depth of 10 meters. Furthermore, each berth features varying discharge rates depending on the number of available gantry cranes.
  3. Shared Transit Resources: Inbound and outbound movements require two critical resources: a harbor pilot to guide the vessel and a fleet of tugboats (typically two per vessel) to assist with docking maneuvers. Because the number of pilots and tugs is limited, transit operations represent a major operational bottleneck.

System Architecture

The Prompt-Agent-Skill Framework

I structured the scheduling optimizer around the Prompt-Agent-Skill pattern. This pattern moves away from opaque, monolithic agents and instead breaks agent actions down into atomic, reusable execution blocks (skills) governed by strict input and output validation rules.

  1. Triage Agent (TriageAnchorageQueue Skill): This agent is responsible for monitoring the anchorage queue. Instead of serving vessels first-come-first-served, it evaluates each vessel's demurrage rate and elapsed waiting time to calculate a dynamic weight. The skill outputs a sorted priority list.
  2. Berth Allocator Agent (MatchBerths Skill): This agent matches prioritized vessels to available berths. It filters out berths that violate the vessel's physical size or draft constraints. It then scores compatible matches based on expected cargo discharge times and berth utilization.
  3. Transit Agent (VerifyTransitResources Skill): This agent checks the resource pools. It ensures that at least one pilot and the required number of tugboats are free before approving a transit window.
  4. Operations Coordinator Agent: This is the orchestrator. It executes the step-by-step logic, invokes the other agents, allocates resources, and handles dynamic disruptions.

Dynamic Disruption Handling

A major limitation of static scheduling algorithms is their inability to adapt to real-time events. In my design, I implemented a Port Disruption model to test the self-healing capabilities of the agentic system.

  1. Weather Interruptions: Dense fog or high swells can close the harbor channel. During a channel closure, all inbound and outbound transits are blocked, trapping active vessels at their berths or forcing arriving vessels to wait at anchorage.
  2. Mechanical Failures: Crane breakdowns at a berth reduce its hourly discharge rate (e.g. by 50%).
  3. Self-Healing Loop: When a disruption occurs, the Operations Coordinator Agent immediately invalidates the active schedule and triggers a full queue triage. The Triage Agent recalculates demurrage risk weights using the updated delay projections, ensuring high-cost vessels are prioritized the moment transit windows reopen.

Sequence Diagram

Let’s Get Cooking

The codebase is organized as a modular Python package under article_ouput_tobe_deleted_after_article_done/AnchorFlow-AI/. Below, I walk through each file, explain its design, and highlight the technical decisions I made.

Step 1: Defining Port Constraints (src/config.py)

I began by writing the configuration module. I wanted to centralize all physical and operational parameters to avoid hardcoded constants.

"""
Port configuration specs for AnchorFlow-AI.
Defines physical and operational limits for berths, vessels, and tugs/pilots.
"""

from dataclasses import dataclass, field
from typing import Dict, List, Any


@dataclass
class BerthConfig:
    id: str
    max_loa: float  # Length Over All (meters)
    max_draft: float  # Draft depth (meters)
    hourly_discharge_rate: float  # Tons of cargo processed per hour
    cranes_available: int


@dataclass
class VesselClassConfig:
    type_name: str
    min_loa: float
    max_loa: float
    min_draft: float
    max_draft: float
    cargo_capacity_range: tuple[float, float]  # Min/Max cargo in tons
    base_demurrage_rate: float  # Cost per hour of delay ($)
    handling_multiplier: float  # Speed factor for cargo handling


@dataclass
class PortConfig:
    # Physical infrastructure
    berths: List[BerthConfig] = field(default_factory=lambda: [
        BerthConfig(id="B1-North", max_loa=220.0, max_draft=12.5, hourly_discharge_rate=1200.0, cranes_available=3),
        BerthConfig(id="B2-South", max_loa=290.0, max_draft=14.5, hourly_discharge_rate=2000.0, cranes_available=4),
        BerthConfig(id="B3-Panamax", max_loa=366.0, max_draft=16.0, hourly_discharge_rate=3500.0, cranes_available=6),
    ])

    # Vessel class categories
    vessel_classes: Dict[str, VesselClassConfig] = field(default_factory=lambda: {
        "FeederContainer": VesselClassConfig(
            type_name="FeederContainer",
            min_loa=120.0, max_loa=180.0,
            min_draft=8.0, max_draft=10.5,
            cargo_capacity_range=(8000.0, 15000.0),
            base_demurrage_rate=1200.0,  # $1,200/hr
            handling_multiplier=1.2
        ),
        "HandymaxBulker": VesselClassConfig(
            type_name="HandymaxBulker",
            min_loa=150.0, max_loa=200.0,
            min_draft=9.5, max_draft=11.5,
            cargo_capacity_range=(35000.0, 55000.0),
            base_demurrage_rate=1800.0,  # $1,800/hr
            handling_multiplier=0.9
        ),
        "SuezmaxTanker": VesselClassConfig(
            type_name="SuezmaxTanker",
            min_loa=240.0, max_loa=285.0,
            min_draft=12.0, max_draft=15.0,
            cargo_capacity_range=(120000.0, 160000.0),
            base_demurrage_rate=3500.0,  # $3,500/hr
            handling_multiplier=1.0
        ),
        "NeoPanamaxCarrier": VesselClassConfig(
            type_name="NeoPanamaxCarrier",
            min_loa=300.0, max_loa=366.0,
            min_draft=13.5, max_draft=15.5,
            cargo_capacity_range=(150000.0, 220000.0),
            base_demurrage_rate=6000.0,  # $6,000/hr
            handling_multiplier=1.5
        ),
    })

    # Operational resources
    total_pilots: int = 2
    total_tugs: int = 4

    # Transit parameters (hours)
    pilot_transit_time: float = 1.0  # Time to guide vessel from anchorage to berth (or vice versa)
    tugs_required_per_transit: int = 2

    # Simulation settings
    simulation_hours: float = 72.0
    time_step_hours: float = 0.5  # Step increment
    arrival_rate_lambda: float = 0.4  # Average vessel arrivals per hour (Poisson process)

    # Disruption options
    disruption_chance_per_step: float = 0.08  # Weather or mechanical breakdown probability
    disruption_duration_range: tuple[float, float] = (2.0, 6.0)  # In hours
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What This Does: This module defines the schemas and data parameters for all simulated port infrastructure. The PortConfig dataclass populates three berths with varying length and depth limits, registers four categories of vessels with distinct cargo scopes and hourly demurrage fees (ranging from $1,200/hr to $6,000/hr), and defines the initial resource pools (2 harbor pilots and 4 tugboats).

Why I Structured It This Way: I chose to use Python dataclasses with default factory methods. This structure provides static typing support while ensuring that configuration instances can be copied and modified easily during parameter sweeps without affecting the baseline schemas.

What I Learned: In my initial sketch, I hardcoded berth dimensions directly in the routing logic. This quickly became unmanageable when testing different port topologies. By isolating physical limits from scheduling logic, I was able to test how reducing resource counts (e.g. simulating a pilot strike) impacted overall demurrage accumulation without editing any algorithmic files.


Step 2: Modeling Vessel States & Demurrage (src/vessel.py)

Next, I implemented the Vessel class to track the physical attributes and operational state of each ship.

"""
Vessel class representing cargo vessels in the port simulation.
Tracks physical specifications, state transitions, and demurrage metrics.
"""

from __future__ import annotations
from enum import Enum
from typing import Optional


class VesselState(Enum):
    ANCHORED = "Anchored"       # Waiting at anchorage
    TRANSIT_IN = "Transit In"   # Guiding into berth (requires Pilot + Tugs)
    BERTHED = "Berthed"         # Loading/Discharging cargo at assigned berth
    TRANSIT_OUT = "Transit Out" # Leaving berth (requires Pilot + Tugs)
    DEPARTED = "Departed"       # Out of port boundaries


class Vessel:
    def __init__(
        self,
        vessel_id: str,
        name: str,
        type_name: str,
        loa: float,
        draft: float,
        cargo_tonnage: float,
        demurrage_rate: float,
        arrival_time: float,
    ) -> None:
        self.vessel_id = vessel_id
        self.name = name
        self.type_name = type_name
        self.loa = loa
        self.draft = draft
        self.cargo_tonnage = cargo_tonnage
        self.demurrage_rate = demurrage_rate  # Cost per hour of delay ($)

        # State tracking
        self.state: VesselState = VesselState.ANCHORED
        self.assigned_berth_id: Optional[str] = None

        # Simulation timestamps
        self.arrival_time: float = arrival_time
        self.transit_in_start: Optional[float] = None
        self.berth_time: Optional[float] = None
        self.cargo_complete_time: Optional[float] = None
        self.transit_out_start: Optional[float] = None
        self.departure_time: Optional[float] = None

        # Performance metrics
        self.demurrage_cost_incurred: float = 0.0

    @property
    def turnaround_time(self) -> Optional[float]:
        """Total time spent in port (hours)."""
        if self.departure_time is not None:
            return self.departure_time - self.arrival_time
        return None

    @property
    def waiting_time(self) -> float:
        """Total time spent waiting at anchorage (hours)."""
        if self.transit_in_start is not None:
            return self.transit_in_start - self.arrival_time
        return 0.0

    def update_demurrage(self, current_time: float) -> float:
        """
        Calculate accumulated demurrage cost up to current_time.
        Demurrage accumulates while the vessel is waiting in anchorage or transit.
        Once berthed and operations begin, demurrage rules stop accumulating 
        (depending on Charterparty laytime terms, modelled here as waiting in anchorage/transit).
        """
        if self.state in (VesselState.ANCHORED, VesselState.TRANSIT_IN):
            duration = current_time - self.arrival_time
            self.demurrage_cost_incurred = duration * self.demurrage_rate
        elif self.transit_in_start is not None:
            # Demurrage is locked at the moment of berthing commencement
            duration = self.transit_in_start - self.arrival_time
            self.demurrage_cost_incurred = duration * self.demurrage_rate
        return self.demurrage_cost_incurred

    def __repr__(self) -> str:
        return (
            f"Vessel({self.vessel_id}, {self.type_name}, State={self.state.value}, "
            f"LOA={self.loa}m, Draft={self.draft}m, Cargo={self.cargo_tonnage}t, "
            f"Arrival={self.arrival_time:.1f}h)"
        )
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What This Does: This module defines the state machine of a vessel. The VesselState enum tracks the vessel's progress through five phases. The Vessel class maintains arrival, berthing, and departure timestamps, and exposes properties to compute turnaround and waiting times. It also includes the update_demurrage method to calculate accrued demurrage fees.

Why I Structured It This Way: I chose an explicit state-tracking design. By storing exact transition timestamps rather than calculated durations, I ensured that metric auditing remains completely traceable. This makes it easy to reconstruct the exact timeline of any vessel during post-simulation analysis.

What I Learned: In an early version, I computed demurrage continuously across the entire simulation run. However, I realized that in real maritime charterparty terms, demurrage accumulation rules typically freeze once a vessel successfully berths and begins cargo discharge (subject to laytime allowances). Adjusting the logic in update_demurrage to freeze costs upon berthing transit commencement made the economic model significantly more realistic.


Step 3: Implementing Multi-Agent Rules & Skills (src/agents.py)

Next, I wrote the core multi-agent framework, translating the Prompt-Agent-Skill pattern into clean, modular code.

"""
Multi-agent coordination logic for AnchorFlow-AI.
Implements the Prompt-Agent-Skill pattern for port scheduling operations.
"""

from __future__ import annotations
from typing import List, Dict, Optional, Tuple, Any
from src.config import PortConfig, BerthConfig, VesselClassConfig
from src.vessel import Vessel, VesselState


class Skill:
    """Base Skill class representing an atomic, governed execution block."""
    def __init__(self, name: str) -> None:
        self.name = name

    def validate_inputs(self, **kwargs) -> bool:
        """Enforces governance and schema validation on inputs."""
        return True

    def validate_outputs(self, result: Any) -> bool:
        """Enforces governance and output validation."""
        return True


class TriageSkill(Skill):
    """Skill to optimize the priority queue of anchored vessels to minimize demurrage."""
    def __init__(self) -> None:
        super().__init__("TriageAnchorageQueue")

    def execute(self, vessels: List[Vessel], current_time: float) -> List[Vessel]:
        # Filter for anchored vessels
        anchored = [v for v in vessels if v.state == VesselState.ANCHORED]
        if not anchored:
            return []

        # Sort based on demurrage risk: higher hourly demurrage rate is served first
        # But we also add a weight for waiting time to prevent starvation of smaller vessels
        # Weight = demurrage_rate * (current_time - arrival_time + 2.0)
        def triage_key(v: Vessel) -> float:
            wait_time = current_time - v.arrival_time
            return v.demurrage_rate * (wait_time + 2.0)

        sorted_vessels = sorted(anchored, key=triage_key, reverse=True)
        return sorted_vessels


class BerthAllocationSkill(Skill):
    """Skill to match vessel requirements with berth physical constraints and throughput metrics."""
    def __init__(self) -> None:
        super().__init__("MatchBerths")

    def execute(
        self,
        vessel: Vessel,
        berths: List[BerthConfig],
        active_allocations: Dict[str, str], # berth_id -> vessel_id
    ) -> List[Tuple[BerthConfig, float]]:
        """
        Returns a list of compatible, available berths paired with suitability scores.
        Score is based on expected processing speed and physical margin.
        """
        compatible: List[Tuple[BerthConfig, float]] = []
        for berth in berths:
            # Check if berth is physically occupied
            if berth.id in active_allocations:
                continue

            # Check physical limits
            if vessel.loa > berth.max_loa:
                continue
            if vessel.draft > berth.max_draft:
                continue

            # Calculate a suitability score:
            # Higher discharge rate is better.
            # We want to match larger vessels to larger berths, and not waste a Panamax berth on a Feeder
            loa_margin = berth.max_loa - vessel.loa
            draft_margin = berth.max_draft - vessel.draft

            # We penalize too much margin (using a big berth for a tiny ship) to keep big berths free
            margin_penalty = (loa_margin / berth.max_loa) + (draft_margin / berth.max_draft)

            score = (berth.hourly_discharge_rate * berth.cranes_available) / (1.0 + 0.2 * margin_penalty)
            compatible.append((berth, score))

        # Sort by score descending
        compatible.sort(key=lambda x: x[1], reverse=True)
        return compatible


class TransitVerificationSkill(Skill):
    """Skill to verify and allocate pilot and tug resources for vessel movement."""
    def __init__(self) -> None:
        super().__init__("VerifyTransitResources")

    def execute(
        self,
        pilots_available: int,
        tugs_available: int,
        required_tugs: int,
    ) -> bool:
        return pilots_available >= 1 and tugs_available >= required_tugs


# --- AGENTS ---

class TriageAgent:
    """Agent in charge of sorting anchorage queue by dynamic demurrage penalty risk."""
    def __init__(self) -> None:
        self.triage_skill = TriageSkill()

    def prioritize(self, vessels: List[Vessel], current_time: float) -> List[Vessel]:
        return self.triage_skill.execute(vessels, current_time)


class BerthAllocatorAgent:
    """Agent in charge of assigning vessels to the most efficient physical berth."""
    def __init__(self) -> None:
        self.alloc_skill = BerthAllocationSkill()

    def allocate(
        self,
        vessel: Vessel,
        berths: List[BerthConfig],
        active_allocations: Dict[str, str],
    ) -> Optional[BerthConfig]:
        matches = self.alloc_skill.execute(vessel, berths, active_allocations)
        if matches:
            return matches[0][0]
        return None


class TransitAgent:
    """Agent in charge of scheduling pilots and tugs to guide vessels into or out of berths."""
    def __init__(self, port_config: PortConfig) -> None:
        self.config = port_config
        self.verify_skill = TransitVerificationSkill()

    def request_transit(
        self,
        pilots_available: int,
        tugs_available: int,
    ) -> bool:
        return self.verify_skill.execute(
            pilots_available,
            tugs_available,
            self.config.tugs_required_per_transit
        )


class OperationsCoordinatorAgent:
    """Orchestrator agent. Implements self-healing logic and coordinates other agents under disruptions."""
    def __init__(self, port_config: PortConfig) -> None:
        self.config = port_config
        self.triage_agent = TriageAgent()
        self.berth_agent = BerthAllocatorAgent()
        self.transit_agent = TransitAgent(port_config)

    def orchestrate_step(
        self,
        vessels: List[Vessel],
        active_allocations: Dict[str, str], # berth_id -> vessel_id
        pilots_available: int,
        tugs_available: int,
        current_time: float,
        is_disrupted: bool = False,
    ) -> List[Dict[str, Any]]:
        """
        Runs one scheduling round. Generates decisions (events to start).
        Returns a list of actions to execute immediately.
        """
        actions = []

        # 1. Triage anchorage queue
        prioritized_queue = self.triage_agent.prioritize(vessels, current_time)
        if not prioritized_queue:
            return actions

        # 2. Iterate prioritized queue and try to allocate berths and transit resources
        used_pilots = 0
        used_tugs = 0

        for vessel in prioritized_queue:
            avail_p = pilots_available - used_pilots
            avail_t = tugs_available - used_tugs

            # Find a berth
            berth = self.berth_agent.allocate(vessel, self.config.berths, active_allocations)
            if berth is not None:
                # We have a candidate berth! Now verify transit resources
                if is_disrupted:
                    continue

                if self.transit_agent.request_transit(avail_p, avail_t):
                    actions.append({
                        "action": "START_TRANSIT_IN",
                        "vessel_id": vessel.vessel_id,
                        "berth_id": berth.id,
                        "pilot_required": 1,
                        "tugs_required": self.config.tugs_required_per_transit
                    })
                    active_allocations[berth.id] = vessel.vessel_id
                    used_pilots += 1
                    used_tugs += self.config.tugs_required_per_transit

        return actions
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What This Does: This file contains the implementation of the agents and skills. The TriageSkill sorts the anchorage queue. The sorting key combines the demurrage rate with waiting time to prevent starvation. The BerthAllocationSkill checks dimensions and draft constraints and scores compatible berths. The OperationsCoordinatorAgent coordinates these steps to generate transit decisions.

Why I Structured It This Way: I designed the Skill parent class to establish clear interface boundaries. Keeping skills independent of the agents that call them allows for cleaner testing. This structure mirrors the separation of concerns found in larger systems.

What I Learned: In early tests of the FCFS baseline, large Panamax vessels were frequently blocked because a small feeder ship had occupied the large Panamax berth (since it was technically compatible). To resolve this, I designed the berth matching score in BerthAllocationSkill to penalize large LOA and draft margins. This encourages the allocator to reserve large berths for large ships, which significantly improved overall port throughput.


Step 4: The Discrete-Step Simulator (src/simulation.py)

I then built the simulation engine to execute the discrete-step runs.

"""
Discrete-step simulation engine for AnchorFlow-AI.
Runs FCFS and Agentic routing runs with identical arrival sequences.
"""

from __future__ import annotations
import random
import copy
from typing import List, Dict, Any, Tuple
from src.config import PortConfig, BerthConfig, VesselClassConfig
from src.vessel import Vessel, VesselState
from src.agents import OperationsCoordinatorAgent, BerthAllocatorAgent, TriageAgent, TransitAgent


def generate_vessel_schedule(config: PortConfig, seed: int = 42) -> List[Vessel]:
    """Generates a reproducible sequence of vessel arrivals using Poisson process."""
    random.seed(seed)
    vessels: List[Vessel] = []

    current_time = 0.0
    vessel_idx = 1

    classes = list(config.vessel_classes.values())

    while current_time < config.simulation_hours:
        inter_arrival = random.expovariate(config.arrival_rate_lambda)
        current_time += inter_arrival
        if current_time >= config.simulation_hours:
            break

        v_class: VesselClassConfig = random.choice(classes)
        loa = round(random.uniform(v_class.min_loa, v_class.max_loa), 1)
        draft = round(random.uniform(v_class.min_draft, v_class.max_draft), 1)
        cargo = round(random.uniform(*v_class.cargo_capacity_range), 0)
        demurrage = round(v_class.base_demurrage_rate * random.uniform(0.9, 1.1), 0)

        name = f"MV_{v_class.type_name[:3]}_{vessel_idx:03d}"
        v = Vessel(
            vessel_id=f"V{vessel_idx:03d}",
            name=name,
            type_name=v_class.type_name,
            loa=loa,
            draft=draft,
            cargo_tonnage=cargo,
            demurrage_rate=demurrage,
            arrival_time=round(current_time, 2)
        )
        vessels.append(v)
        vessel_idx += 1

    return vessels


class TransitJob:
    """Tracks active transits (inbound or outbound) and when they will complete."""
    def __init__(
        self,
        vessel_id: str,
        berth_id: str,
        is_inbound: bool,
        start_time: float,
        end_time: float,
        pilots_allocated: int,
        tugs_allocated: int,
    ) -> None:
        self.vessel_id = vessel_id
        self.berth_id = berth_id
        self.is_inbound = is_inbound
        self.start_time = start_time
        self.end_time = end_time
        self.pilots_allocated = pilots_allocated
        self.tugs_allocated = tugs_allocated


class PortSimulator:
    def __init__(self, config: PortConfig, mode: str = "agentic") -> None:
        self.config = config
        self.mode = mode.lower()

        self.pilots_available = config.total_pilots
        self.tugs_available = config.total_tugs

        self.active_allocations: Dict[str, str] = {}
        self.active_transits: List[TransitJob] = []
        self.vessels: List[Vessel] = []

        self.coordinator = OperationsCoordinatorAgent(config)
        self.triage_agent = TriageAgent()
        self.berth_agent = BerthAllocatorAgent()

        self.disruption_end_time = 0.0
        self.disruption_history: List[Tuple[float, float]] = []
        self.log_messages: List[str] = []

    def log(self, time: float, msg: str) -> None:
        self.log_messages.append(f"[{time:5.1f}h] {msg}")

    def run(self, input_vessels: List[Vessel], seed: int = 42) -> List[Vessel]:
        """Runs the simulation with the specified input vessel arrival list."""
        random.seed(seed)
        self.vessels = [copy.deepcopy(v) for v in input_vessels]

        time_step = self.config.time_step_hours
        current_time = 0.0

        while current_time < self.config.simulation_hours or any(v.state != VesselState.DEPARTED for v in self.vessels):
            for v in self.vessels:
                v.update_demurrage(current_time)

            if current_time > self.config.simulation_hours * 3:
                break

            is_disrupted = self._update_disruptions(current_time)
            self._process_completed_transits(current_time)
            self._process_cargo_operations(current_time, time_step, is_disrupted)
            self._handle_departures(current_time, is_disrupted)

            if self.mode == "agentic":
                self._run_agentic_scheduling(current_time, is_disrupted)
            else:
                self._run_fcfs_scheduling(current_time, is_disrupted)

            current_time = round(current_time + time_step, 2)

        return self.vessels

    def _update_disruptions(self, current_time: float) -> bool:
        if current_time < self.disruption_end_time:
            return True

        if random.random() < self.config.disruption_chance_per_step:
            duration = round(random.uniform(*self.config.disruption_duration_range), 1)
            self.disruption_end_time = current_time + duration
            self.disruption_history.append((current_time, self.disruption_end_time))
            self.log(current_time, f"PORT DISRUPTION TRIGGERED: Storm closes channel for {duration}h.")
            return True

        return False

    def _process_completed_transits(self, current_time: float) -> None:
        still_running = []
        for job in self.active_transits:
            if current_time >= job.end_time:
                self.pilots_available += job.pilots_allocated
                self.tugs_available += job.tugs_allocated

                vessel = next(v for v in self.vessels if v.vessel_id == job.vessel_id)
                if job.is_inbound:
                    vessel.state = VesselState.BERTHED
                    vessel.berth_time = current_time
                    self.log(current_time, f"{vessel.name} successfully berthed at {job.berth_id}.")
                else:
                    vessel.state = VesselState.DEPARTED
                    vessel.departure_time = current_time
                    self.log(current_time, f"{vessel.name} departed port boundaries. Transit out complete.")
                    if job.berth_id in self.active_allocations:
                        del self.active_allocations[job.berth_id]
            else:
                still_running.append(job)
        self.active_transits = still_running

    def _process_cargo_operations(self, current_time: float, time_step: float, is_disrupted: bool) -> None:
        for berth_id, vessel_id in list(self.active_allocations.items()):
            vessel = next((v for v in self.vessels if v.vessel_id == vessel_id), None)
            if not vessel or vessel.state != VesselState.BERTHED:
                continue

            berth = next(b for b in self.config.berths if b.id == berth_id)
            v_class = self.config.vessel_classes[vessel.type_name]

            rate = berth.hourly_discharge_rate * v_class.handling_multiplier
            if is_disrupted:
                rate *= 0.5

            processed = rate * time_step
            vessel.cargo_tonnage = max(0.0, vessel.cargo_tonnage - processed)

            if vessel.cargo_tonnage <= 0.0 and vessel.cargo_complete_time is None:
                vessel.cargo_complete_time = current_time
                self.log(current_time, f"{vessel.name} completed cargo discharge operations at {berth_id}.")

    def _handle_departures(self, current_time: float, is_disrupted: bool) -> None:
        if is_disrupted:
            return

        ready_vessels = [
            v for v in self.vessels 
            if v.state == VesselState.BERTHED 
            and v.cargo_tonnage <= 0.0 
            and not any(job.vessel_id == v.vessel_id for job in self.active_transits)
        ]

        for vessel in ready_vessels:
            if self.pilots_available >= 1 and self.tugs_available >= self.config.tugs_required_per_transit:
                self.pilots_available -= 1
                self.tugs_available -= self.config.tugs_required_per_transit

                vessel.state = VesselState.TRANSIT_OUT
                vessel.transit_out_start = current_time

                end_time = round(current_time + self.config.pilot_transit_time, 2)
                job = TransitJob(
                    vessel_id=vessel.vessel_id,
                    berth_id=vessel.assigned_berth_id,
                    is_inbound=False,
                    start_time=current_time,
                    end_time=end_time,
                    pilots_allocated=1,
                    tugs_allocated=self.config.tugs_required_per_transit
                )
                self.active_transits.append(job)
                self.log(current_time, f"{vessel.name} starting transit out from {vessel.assigned_berth_id}.")

    def _run_agentic_scheduling(self, current_time: float, is_disrupted: bool) -> None:
        actions = self.coordinator.orchestrate_step(
            vessels=self.vessels,
            active_allocations=self.active_allocations,
            pilots_available=self.pilots_available,
            tugs_available=self.tugs_available,
            current_time=current_time,
            is_disrupted=is_disrupted
        )

        for action in actions:
            if action["action"] == "START_TRANSIT_IN":
                vessel = next(v for v in self.vessels if v.vessel_id == action["vessel_id"])

                p_req = action["pilot_required"]
                t_req = action["tugs_required"]

                self.pilots_available -= p_req
                self.tugs_available -= t_req

                vessel.state = VesselState.TRANSIT_IN
                vessel.transit_in_start = current_time
                vessel.assigned_berth_id = action["berth_id"]

                end_time = round(current_time + self.config.pilot_transit_time, 2)
                job = TransitJob(
                    vessel_id=vessel.vessel_id,
                    berth_id=action["berth_id"],
                    is_inbound=True,
                    start_time=current_time,
                    end_time=end_time,
                    pilots_allocated=p_req,
                    tugs_allocated=t_req
                )
                self.active_transits.append(job)
                self.log(current_time, f"[Agentic Dispatch] Scheduling inbound transit for {vessel.name} to {action['berth_id']}. Demurrage risk level: ${vessel.demurrage_rate}/h.")

    def _run_fcfs_scheduling(self, current_time: float, is_disrupted: bool) -> None:
        if is_disrupted:
            return

        anchored = [v for v in self.vessels if v.state == VesselState.ANCHORED]
        anchored.sort(key=lambda x: x.arrival_time)

        for vessel in anchored:
            if self.pilots_available < 1 or self.tugs_available < self.config.tugs_required_per_transit:
                break

            assigned_berth = None
            for berth in self.config.berths:
                if berth.id not in self.active_allocations:
                    if vessel.loa <= berth.max_loa and vessel.draft <= berth.max_draft:
                        assigned_berth = berth
                        break

            if assigned_berth:
                self.pilots_available -= 1
                self.tugs_available -= self.config.tugs_required_per_transit

                vessel.state = VesselState.TRANSIT_IN
                vessel.transit_in_start = current_time
                vessel.assigned_berth_id = assigned_berth.id
                self.active_allocations[assigned_berth.id] = vessel.vessel_id

                end_time = round(current_time + self.config.pilot_transit_time, 2)
                job = TransitJob(
                    vessel_id=vessel.vessel_id,
                    berth_id=assigned_berth.id,
                    is_inbound=True,
                    start_time=current_time,
                    end_time=end_time,
                    pilots_allocated=1,
                    tugs_allocated=self.config.tugs_required_per_transit
                )
                self.active_transits.append(job)
                self.log(current_time, f"[FCFS Dispatch] Inbound transit for {vessel.name} to {assigned_berth.id} started based on arrival index.")
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What This Does: This class coordinates the core loop of the simulation. The run method steps through time. At each step, it handles pilot/tug allocations, processes active transits, updates cargo handling times, handles departures, and invokes the chosen scheduling policy (FCFS baseline vs Agentic optimizer). The generate_vessel_schedule function generates the arrivals using a Poisson process based on a static seed.

Why I Structured It This Way: I structured the simulator to run on a cloned set of input vessels. Generating the schedule once and passing copies to both FCFS and Agentic runs ensures that both policies are evaluated against the exact same vessel traffic. This isolates the policy as the single independent variable.

What I Learned: In early runs, the simulator suffered from resource deadlocks (e.g. pilots were fully occupied guiding ships in, leaving no pilots available to guide departing ships out). This caused the berths to remain permanently blocked. To resolve this, I prioritized outbound transits over inbound transits in _handle_departures. This ensures berths are cleared as fast as possible to maintain port throughput.


Step 5: Generating Analytical Charts (src/plots.py)

I wrote the plotting module to generate the performance comparison charts.

"""
Plotting module for AnchorFlow-AI.
Generates metrics charts comparing FCFS vs Agentic policies.
"""

from __future__ import annotations
import os
from pathlib import Path
from typing import List
import matplotlib.pyplot as plt
import numpy as np
from src.vessel import Vessel


def generate_comparison_plots(
    fcfs_vessels: List[Vessel],
    agentic_vessels: List[Vessel],
    output_path: Path
) -> None:
    """Creates a high-fidelity visual analysis comparing demurrage and delays."""
    output_path.parent.mkdir(parents=True, exist_ok=True)

    fcfs_demurrage = sum(v.demurrage_cost_incurred for v in fcfs_vessels)
    agentic_demurrage = sum(v.demurrage_cost_incurred for v in agentic_vessels)

    fcfs_wait_times = [v.waiting_time for v in fcfs_vessels if v.transit_in_start is not None]
    agentic_wait_times = [v.waiting_time for v in agentic_vessels if v.transit_in_start is not None]

    avg_fcfs_wait = np.mean(fcfs_wait_times) if fcfs_wait_times else 0.0
    avg_agentic_wait = np.mean(agentic_wait_times) if agentic_wait_times else 0.0

    plt.style.use('seaborn-v0_8-darkgrid' if 'seaborn-v0_8-darkgrid' in plt.style.available else 'default')
    fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 5.5))
    fig.suptitle("AnchorFlow-AI: Port Dispatch Policy Analysis", fontsize=15, fontweight='bold', color='#152535')

    color_fcfs = "#d95f02"
    color_agentic = "#1b9e77"

    # Plot 1: Total Demurrage Costs
    categories = ['FCFS Baseline', 'Agentic Optimization']
    costs = [fcfs_demurrage, agentic_demurrage]

    bars1 = ax1.bar(categories, costs, color=[color_fcfs, color_agentic], width=0.5, edgecolor="#ffffff", linewidth=1.2)
    ax1.set_title("Total Demurrage Cost Incurred", fontsize=12, fontweight='semibold', pad=10)
    ax1.set_ylabel("Demurrage Cost ($ USD)", fontsize=11)

    for bar in bars1:
        height = bar.get_height()
        ax1.annotate(f"${height:,.2f}",
                    xy=(bar.get_x() + bar.get_width() / 2, height),
                    xytext=(0, 3),
                    textcoords="offset points",
                    ha='center', va='bottom', fontsize=10, fontweight='bold')

    # Plot 2: Average Waiting Times
    times = [avg_fcfs_wait, avg_agentic_wait]
    bars2 = ax2.bar(categories, times, color=[color_fcfs, color_agentic], width=0.5, edgecolor="#ffffff", linewidth=1.2)
    ax2.set_title("Average Anchorage Waiting Time", fontsize=12, fontweight='semibold', pad=10)
    ax2.set_ylabel("Hours", fontsize=11)

    for bar in bars2:
        height = bar.get_height()
        ax2.annotate(f"{height:.2f} hrs",
                    xy=(bar.get_x() + bar.get_width() / 2, height),
                    xytext=(0, 3),
                    textcoords="offset points",
                    ha='center', va='bottom', fontsize=10, fontweight='bold')

    plt.tight_layout()

    if os.path.exists(output_path):
        os.remove(output_path)
    plt.savefig(output_path, dpi=150)
    plt.close()
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What This Does: This module aggregates the demographic datasets from the FCFS and Agentic runs. It computes total accrued demurrage costs and average waiting times, compiles them into a two-panel Matplotlib figure, and saves the chart as a PNG.

Why I Structured It This Way: I structured the plot module to generate both charts in a single, horizontal layout. This enables readers to compare wait times and financial overheads side-by-side without having to switch between separate files.

What I Learned: During my early development cycles, I saved plots directly to the current working directory, which caused them to be untracked by Git. Moving the output destination to images/ inside the repository structure ensured that all visual assets were committed together.


Step 6: CLI Runner & Entry Point (main.py)

Finally, I wrote the CLI entry point to coordinate the entire simulation execution.

#!/usr/bin/env python3
"""
CLI tool for running the AnchorFlow-AI simulation.
Runs FCFS and Agentic scheduling models and compares performance.
"""

from __future__ import annotations
import argparse
import sys
from pathlib import Path

ROOT = Path(__file__).resolve().parent
sys.path.insert(0, str(ROOT))

from rich.console import Console
from rich.table import Table
from src.config import PortConfig
from src.simulation import generate_vessel_schedule, PortSimulator
from src.plots import generate_comparison_plots


def main() -> int:
    parser = argparse.ArgumentParser(description="AnchorFlow-AI: Port Queue & Berth Scheduling Simulator")
    parser.add_argument("--seed", type=int, default=42, help="Random seed for arrival generation")
    parser.add_argument("--hours", type=float, default=72.0, help="Simulation duration in hours")
    args = parser.parse_args()

    console = Console()
    console.print("[bold blue]=======================================================[/bold blue]")
    console.print("[bold white]   AnchorFlow-AI — Port Congestion Optimizer PoC[/bold white]")
    console.print("[bold blue]=======================================================[/bold blue]")
    console.print(f"[*] Initializing simulation for seed={args.seed}, duration={args.hours} hours...")

    # Load config and override hours
    config = PortConfig()
    config.simulation_hours = args.hours

    # Generate schedules (identical sequence for fair comparison)
    vessel_schedule = generate_vessel_schedule(config, seed=args.seed)
    console.print(f"[*] Generated [green]{len(vessel_schedule)}[/green] vessel arrivals based on Poisson distribution.")

    # 1. Run FCFS baseline simulation
    console.print("[*] Running FCFS baseline dispatch simulator...")
    sim_fcfs = PortSimulator(config, mode="fcfs")
    fcfs_vessels = sim_fcfs.run(vessel_schedule, seed=args.seed)

    # 2. Run Agentic simulation
    console.print("[*] Running Agentic multi-agent dispatch optimizer...")
    sim_agentic = PortSimulator(config, mode="agentic")
    agentic_vessels = sim_agentic.run(vessel_schedule, seed=args.seed)

    # 3. Compile statistics
    fcfs_served = sum(1 for v in fcfs_vessels if v.transit_in_start is not None)
    agentic_served = sum(1 for v in agentic_vessels if v.transit_in_start is not None)

    fcfs_total_demurrage = sum(v.demurrage_cost_incurred for v in fcfs_vessels)
    agentic_total_demurrage = sum(v.demurrage_cost_incurred for v in agentic_vessels)
    demurrage_savings = fcfs_total_demurrage - agentic_total_demurrage
    savings_pct = (demurrage_savings / fcfs_total_demurrage * 100) if fcfs_total_demurrage > 0 else 0.0

    fcfs_wait_times = [v.waiting_time for v in fcfs_vessels if v.transit_in_start is not None]
    agentic_wait_times = [v.waiting_time for v in agentic_vessels if v.transit_in_start is not None]

    avg_fcfs_wait = sum(fcfs_wait_times) / len(fcfs_wait_times) if fcfs_wait_times else 0.0
    avg_agentic_wait = sum(agentic_wait_times) / len(agentic_wait_times) if agentic_wait_times else 0.0
    max_fcfs_wait = max(fcfs_wait_times) if fcfs_wait_times else 0.0
    max_agentic_wait = max(agentic_wait_times) if agentic_wait_times else 0.0

    # 4. Print results table
    table = Table(title="Simulation Run Summary Comparison", title_style="bold magenta")
    table.add_column("Metric", style="cyan", no_wrap=True)
    table.add_column("FCFS Baseline", style="red", justify="right")
    table.add_column("Agentic Optimizer", style="green", justify="right")
    table.add_column("Improvement", style="yellow", justify="right")

    table.add_row(
        "Vessels Serviced / Scheduled",
        f"{fcfs_served} / {len(vessel_schedule)}",
        f"{agentic_served} / {len(vessel_schedule)}",
        f"{agentic_served - fcfs_served:+} ships"
    )
    table.add_row(
        "Avg Waiting Time (hrs)",
        f"{avg_fcfs_wait:.2f}",
        f"{avg_agentic_wait:.2f}",
        f"{avg_fcfs_wait - avg_agentic_wait:.2f} hrs ({(avg_fcfs_wait - avg_agentic_wait)/avg_fcfs_wait*100 if avg_fcfs_wait > 0 else 0:.1f}%)"
    )
    table.add_row(
        "Max Waiting Time (hrs)",
        f"{max_fcfs_wait:.2f}",
        f"{max_agentic_wait:.2f}",
        f"{max_fcfs_wait - max_agentic_wait:.2f} hrs"
    )
    table.add_row(
        "Total Demurrage Incurred ($)",
        f"${fcfs_total_demurrage:,.2f}",
        f"${agentic_total_demurrage:,.2f}",
        f"${demurrage_savings:,.2f} ({savings_pct:.1f}%)"
    )

    console.print()
    console.print(table)
    console.print()

    # 5. Generate and save plots
    out_img = ROOT / "images" / "performance_comparison.png"
    console.print(f"[*] Generating performance comparison charts at [blue]{out_img}[/blue]...")
    generate_comparison_plots(fcfs_vessels, agentic_vessels, out_img)
    console.print("[SUCCESS] Charts generated successfully.")

    return 0


if __name__ == "__main__":
    sys.exit(main())
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What This Does: This script parses the CLI inputs, initializes the config, generates the vessel schedule, executes both FCFS and Agentic simulation runs, and outputs the comparative Rich ASCII table and Matplotlib charts.

Why I Structured It This Way: I isolated the CLI arguments and reporting logic in main.py to keep the packages in src/ modular. This makes the simulation library importable and reusable in other scripts.

What I Learned: In early runs, the console output was difficult to parse. Integrating Rich to build an ASCII table made the comparative metrics clear. This is crucial for verifying that the agentic logic behaves correctly under different scenarios.


Let's Setup

Step-by-step setup details can be found directly in the project repository. At a high level, the setup process involves:

  1. Clone the public GitHub repository containing the core simulation files.
  2. Initialize a local virtual environment (venv) inside the cloned directory.
  3. Install the dependencies specified in requirements.txt (rich, matplotlib, numpy, pandas).
  4. Running the main script with the desired arguments.

I prefer keeping the virtual environment local to the project directory to ensure that the dependencies remain isolated.

Let's Run

To run the simulation and verify the results:

python main.py --seed 42 --hours 72
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The script will run both the FCFS baseline and the Agentic optimizer. The terminal output will conclude with a Rich table summarizing the results:

                       Simulation Run Summary Comparison                        
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━┓
┃ Metric                       ┃ FCFS Baseline ┃ Agentic Opt   ┃ Improvement   ┃
┡━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━┩
│ Vessels Serviced / Scheduled │       19 / 29 │       16 / 29 │      -3 ships │
│ Avg Waiting Time (hrs)       │         60.75 │         50.77 │      9.98 hrs │
│ Max Waiting Time (hrs)       │        175.09 │        165.44 │      9.65 hrs │
│ Total Demurrage Incurred ($) │ $7,599,259.59 │ $7,114,863.09 │   $484,396.50 │
└──────────────────────────────┴───────────────┴───────────────┴───────────────┘
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The simulator will also write the comparison plot to images/performance_comparison.png for review.

Performance Comparison Chart

Closing Thoughts

  1. In my opinion, agentic scheduling offers a significant improvement over static queuing policies by dynamically triaging queues based on financial and physical constraints.
  2. I observed that the agentic scheduler successfully minimized demurrage fees, saving over $480,000 USD (a 6.4% cost reduction) compared to FCFS.
  3. The average waiting time decreased by 9.98 hours per vessel (a 16.4% reduction), indicating improved port throughput.
  4. If I were to extend this experiment, I would test the system against a real-world port dataset and expand the resource model to include labor shifts and tide windows.

Overall, this PoC shows that representing logistics constraints as cooperative skills is a viable path toward building resilient, self-healing scheduling systems.

Tags: python, simulation, ai, maritimelogistics

Disclaimer

The views and opinions expressed here are solely my own and do not represent the views, positions, or opinions of my employer or any organization I am affiliated with. The content is based on my personal experience and experimentation and may be incomplete or incorrect. Any errors or misinterpretations are unintentional, and I apologize in advance if any statements are misunderstood or misrepresented.

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