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Optimizing the Hydrodynamic Efficiency of Fishing Vessels: The Art of Minimizing Fuel Costs.




Introduction

The efficiency of a fishing vessel is inextricably linked to its fuel costs. One of the key aspects that determines these costs is the water resistance of the vessel. The lower this resistance, the more efficient the vessel is. In this article we will look at methods for optimizing the shape of a ship's hull to minimize water resistance and, as a result, save fuel.

 

Optimization methods

 

1. Model Test

Throughout the history of shipbuilding, model tank testing has been the standard method for assessing the hydrodynamic characteristics of a ship's hull. These tests make it possible to recalculate the resistance of the model to a full-scale vessel and determine its effectiveness. Despite its reliability, this method requires significant time and financial costs. The undoubted advantages of this method include the high reliability of the experimental results and the possibility of conducting a whole cycle of tests of the ship model at different speeds and under different load conditions.

The disadvantages of this method are the high labor intensity of making the model, the limited possibility of making changes to the shape of the body, and the high cost of conducting the experiment.

 2. CFD (Computational Fluid Dynamics)

Modern technologies provide more effective methods for assessing the hydrodynamic characteristics of a vessel. The CFD computer modeling method allows you to accurately analyze the behavior of a vessel in water, while providing additional data compared to model tests.


The advantages of this method are:

-the ability to quickly prepare and modify a mathematical model of the hull, which is especially important for the optimization process,

- comparatively low cost of calculations and the ability to test a large number of variations in hull shape,

-various options for presenting calculation results.

Disadvantages include high sensitivity to a poorly smoothed hull surface and an incorrectly defined computational mesh.

 

Optimization process.

The process of optimizing the surface of a ship's hull begins with analyzing the results of flow around the hull. Both model tests and computer simulations provide various options for presenting experimental results. CFD calculations make it possible to visualize the dynamic component of pressures around the ship's hull. Areas of high and low pressure are created by the flow of water, which forms a wave pattern.

Changing the shape of the hull allows optimizing this pressure distribution and therefore reducing wave resistance. In practice, the shape of the bow and bulbous bow contributes a significant part to the overall resistance of the vessel.

Let's look at an example of modifying the bow end to optimize the shape of the ship's hull. Changing the shape of the bow waterlines, frames and stem profile allows you to control the formation of the bow wave and minimize its impact on the overall resistance of the vessel. With a well-chosen shape of the bow contours, it is also possible to achieve the effect of damping the bow wave by a system of waves formed in the area where the waterline meets the flat side.



This also reduces wave resistance. Similar rules can be applied when optimizing the stern end. Visualization of the zones of the dynamic component of pressure, the wave pattern around the vessel and streamlines gives a good idea of the process of flow around the hull. Visualization of the associated flow in the propeller disk simultaneously allows you to control the operating conditions of the propeller when changing the shape of the hull.


The resistance of the ship's hull is significantly influenced by the shape of the bow. Significant gains in minimizing drag can be achieved by modifying the bow waterlines and the shape of the bow bulb.



This allows you to control the formation of the bow wave and minimize its impact on the vessel's resistance. Optimization of the stern end is also important. In addition to reducing resistance, it is also necessary to take into account the operating conditions of the propeller.

Summarizing the above, we can conclude that the study of hull resistance in the tank test can only be used for final confirmation of the results of designing the ship's surface. Optimization in an experimental pool is only possible if there is an unlimited budget and a significant amount of time for optimization. The most effective way to optimize is to use CFD methods. In addition to the calculation of the towing resistance of a vessel in calm water, which has already become familiar to most design companies, CFD techniques make it possible to simulate almost any situation, such as:

- simulation of a self propelled ship,

- simulation of ship behavior on a wave,

- simulation of vessel behavior in circulation,

- simulation the operation of pitch stabilizers,

- study of the interaction of the ship's hull with the propeller.



In this case, the most natural design and optimization strategy looks like this:

- creation of a mathematical model of the surface,

- run the model in CFD,

- modification of the hull shape based on the results of the run,

- repeated runs and modifications at each turn of the design spiral of the design process,

- confirmation of CFD calculations by running the model in the tank.

 

During the design process, the surface of the body may change into the model. It is important that all surface changes are verified by CFD calculations. This approach will make it possible to control the hydrodynamic characteristics of the hull at all stages of the project.

 

The process of hull optimization usually takes some time, so it is very important to combine it with the vessel design process. As a rule, changes in the shape of the hull during optimization are not so significant and cannot greatly influence other design characteristics. Once optimization is complete, the surface can be updated for all other participants in the design process.

 

Running the model in the tank is usually decision of the ship owner. This occurs at one of the final stages of the project and is a confirmation of the hull characteristics obtained using CFD calculations.

 

Economic effect

Optimizing the hull shape and improving the operating conditions of the propeller can reduce the ship's drag by 10-15% if a close prototype was used at the initial stages of design. If the original prototype was not good enought, you can win up to 25%. Many customers of new fishing vessels require CFD optimization to be included in the design package. In practice, vessels optimized using CFD exhibit good hydrodynamic performance. This gives shipowners significant fuel savings and reduces harmful emissions into the environment.

 

Conclusion

Hydrodynamic optimization is an integral part of the design of modern fishing vessels. Thanks to modern analysis methods and high-precision technologies, developers can create ships with optimal hydrodynamic characteristics, which helps save fuel and reduce the negative impact on the environment.

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