conceptual_model.md

# Conceptual Model Design

## System Boundary
The model encompasses the haulage operations from the truck parking area to the ore faces (North Pit and South Pit), the transport of ore to the primary crusher, and the return trips. It includes trucks, road segments, loaders, and the crusher. It excludes operations prior to loading (e.g., drilling, blasting), maintenance activities (unless routing through them is forced), waste dumping (the objective focuses on ore to crusher), and downstream processing after the crusher. The simulation covers a single 8-hour shift.

## Entities
- **Trucks**: Active entities that move through the mine topology, carrying ore payloads from loaders to the crusher. They transition between states: travelling empty, queueing for loader, loading, travelling loaded, queueing for crusher, and dumping.

## Resources
- **Loaders**: Constrained resources (capacity=1) located at `LOAD_N` and `LOAD_S`.
- **Crusher**: Constrained resource (capacity=1) located at `CRUSH`.
- **Road Segments**: Capacity-constrained road segments are modelled as resources. Based on edge data, segments like `E03_UP`, `E03_DOWN` (narrow ramps), `E07_TO_LOAD_N`, `E07_FROM_LOAD_N`, `E09_TO_LOAD_S`, `E09_FROM_LOAD_S` (single-lane pit roads), and `E05_TO_CRUSH`, `E05_FROM_CRUSH` (crusher approach) have a capacity of 1, meaning they can only be occupied by one truck at a time, serving as shared constrained resources.

## Events
- **Truck Dispatched**: Truck leaves the parking area at the start of the shift.
- **Travel to Loader**: Truck traverses road segments to reach assigned loader.
- **Join Loader Queue**: Truck arrives at loader node and waits if the loader is busy.
- **Loading Starts**: Truck secures the loader.
- **Loading Ends**: Truck finishes loading payload.
- **Travel to Crusher**: Truck traverses road segments towards the crusher.
- **Join Crusher Queue**: Truck arrives at crusher node and waits if it is busy.
- **Dumping Starts**: Truck secures the crusher.
- **Dumping Ends**: Truck finishes dumping, recording delivered tonnes, and completes a cycle.
- **Return Travel**: Truck travels empty back to a loader.

## State Variables
- **Truck State**: Current location, loaded/empty status.
- **Resource State**: Busy/idle status, queue lengths for loaders, crusher, and constrained road segments.
- **Performance Trackers**: Total tonnes delivered, start/end times of cycles, cumulative busy time for resources.

## Assumptions
### Derived from Data
- Loading and dumping times follow a normal distribution based on provided mean and standard deviation.
- Travel speeds are affected by empty vs loaded factors defined in `trucks.csv`.
- Topologies form a directed graph; unavailable edges (if `closed=True`) are removed.

### Introduced
- **Stochastic Bounds**: Truncated normal distributions for service times are bounded strictly above 0 (e.g., min 0.1 minutes) to prevent non-physical negative times.
- **Travel Noise**: Stochastic travel times have a Coefficient of Variation (CV) of 10% applied as a normal distribution noise.
- **Road Segment Occupation**: A truck requests a constrained road segment resource before entering and releases it upon exiting.

### Limitations
- Acceleration/deceleration kinematics are not explicitly modelled; uniform average travel speeds are assumed.
- Interactions at unconstrained junctions are simplified; trucks pass without intersection logic delays.
- Dispatch logic is greedy (myopic), deciding the next destination based on current state rather than global optimal scheduling.

## Performance Measures
- **Total Tonnes Delivered**: Sum of payloads successfully dumped at the crusher.
- **Tonnes Per Hour**: Total tonnes divided by the shift length (8 hours).
- **Average Truck Cycle Time**: Mean duration from leaving a loader/parking until finishing the dump at the crusher.
- **Truck Utilisation**: Percentage of shift time a truck spends active (travelling, queueing, loading, dumping).
- **Crusher / Loader Utilisation**: Percentage of shift time the resource is busy processing a truck.
- **Queue Times**: Mean time spent waiting in front of loaders and the crusher.