Energy system modelling and optimisation of inland vessel

As the maritime industry moves toward sustainability, energy efficiency in inland vessels has become a critical focus. Inland vessels, including ferries and barges, often operate in constrained waterways where energy consumption needs to be optimised for both environmental and economic reasons. This requires a comprehensive analysis of how the energy system should be modelled and dynamic engine optimisation.  In this blog we will discuss a bit of the two aspects.

What is a ship energy performance model?

A ship performance model serves as an effective tool for simulating and analysing a vessel’s energy system by accounting for the desired sailing speed and its interaction with dynamic water conditions, commonly referred to as the speed-power relationship. Typically, this model is holistic, incorporating components such as hull design, resistance estimation, propeller modelling, and dynamic power prediction. Figure 1 illustrates a performance model for an inland vessel, highlighting the key components of the energy system. By computing the interactions between different modules, the model effectively captures the speed-power characteristics according to the dynamic environment.

Figure 1. Overview of ship performance model of inland vessel [1].

Model validation

A British statistician, George Box, wrote the famous line, “All models are wrong, some are useful.” A model based on physics and extensive empirical formulas must be validated to ensure its reliability. Here, we use power measurement data from a real 3000 DWT inland chemical tanker for validation, as shown in Figure 2. While simulations do not always perfectly replicate real-world conditions, it is important to remember that a ship’s power system is highly complex! Despite using only a limited set of input parameters, the model can still capture the vessel’s power characteristics with reasonable accuracy in constrained waterways.

Figure 2. Power prediction against measurement.

How to optimise the engine

Engine load optimisation for inland vessels focuses on dynamically managing the power output of the propulsion system to achieve maximum fuel efficiency and minimize emissions. Since inland vessels often operate in constrained waterways with varying water depths, currents, and traffic conditions, maintaining an optimal engine load is crucial to ensuring energy-efficient navigation.

In an ongoing study, we have utilized a genetic algorithm (GA) to directly optimize the propeller revolution speed at different locations based on the river profile (see Figures 3 and 4). By adopting the performance model, a response surface is quickly generated to determine the power demand at each waypoint. The GA algorithm then simulates the optimal propeller revolution speed sequence along the voyage (Figure 5).

Figure 3. Example of depth profile of a river segment.

Figure 4. Schematics of propeller revolution speed optimisation.

Figure 5. Optimisation result of surge and sway speed, left (constant engine speed), right (with GA optimisation).

This method is currently being tested across various river segments and current conditions, with preliminary results indicating a potential fuel savings of over 5% through speed optimization.

An article by Chengqian Zhang.

References

Cover Figure. Vessel CADENSIA, source (google).

[1] Zhang C, Ringsberg JW, Thies F. Development of a ship performance model for power estimation of inland waterway vessels. Ocean Engineering. 2023 Nov 1;287:115731.