The hull is the main part of the ship or marine vessel that comes in contact with the fluid.
An ideal hull form reduces drag while improving the speed, efficiency, and maneuverability of the ship in varying marine conditions.
CFD simulation facilitates running multiple iterations of the interaction between the marine structure and the fluid to identify the acting hydrodynamic forces until the ideal hull form optimization parameter is found.
Model of a ship used in hull form optimization
The main body of a ship or marine vessel that comes in contact with the water is the hull. It functions to cover and protect the inner spaces, machinery, and components of the ship, but that is not all it does. It also serves to provide structural support, reduce drag and vibration, and ensure the buoyancy and stability of the ship.
However, the behavior of fluid flow around the ship’s hull significantly impacts how the functionalities of the hull are materialized. Marine engineers need to look at different hull form options or hull form optimization procedures to meet the desired performance specification under different marine conditions. In this article, we will take a look at how the computation fluid dynamic (CFD) approach to hull form optimization can enable the enhancement of the ship’s hydrodynamic performance.
Importance of a Well-Designed Hull
The hull is a critical component, the design of which is directly related to the performance, efficiency, and safety of the ship. A well-designed hull indicates:
Quality of a Well-Designed Hull
Desired Design Feature
Smooth and curved hull
Improved buoyancy and stability
Wider hull and larger cross-section
Sharper and narrower bow (forward-most point of the hull)
Narrow hull with sharp bows
These design features ensure the hydrodynamic efficiency of the ship by improving speed and reducing fuel consumption. The selection of these design features or hull forms, however, has to be done carefully to meet the specific performance requirements for different types of ships and vessels. The following are the most common type of hull forms:
Different Types of Hull Forms
Round bilge hull
Hard chine hull
The understanding of these different hull forms, their interaction with the fluid, and the induced fluid behavior are important in identifying the optimization criteria to achieve the best possible outcome.
The Process of Hull Form Optimization
The process of hull form optimization involves the analysis of the ship’s operational parameters based on the stability and efficiency desired. This includes the evaluation of fluid flow patterns and hydrodynamic resistance around the ship’s hull so as to identify the optimal hull design features. CFD is an effective tool in simplifying the hull form optimization process through effective simulation. It involves the following steps:
Creating a model of the hull geometry.
Meshing the geometry into finite smaller cells such that it captures all the flow features.
Defining the boundary conditions – specify the velocity, pressure, and other properties of the fluid acting on the hull surface.
Performing the simulation. Using the Navier-Stokes equation, the flow field around the hull is identified. Visualization further facilitates the exploration of flow patterns and the calculation of resistance and propulsion forces.
Based on the results from the simulation, the hull forms can be optimized for better performance and efficiency. The simulation can be re-run until the optimal variation of the hull design is identified. For further performance improvement, CFD simulation can also be utilized for analyzing different propeller designs - their shape and position.
Computational Analysis for Hull Form Optimization
Hull form simulation for analyzing fluid-structure interactions
CFD solvers such as Fidelity and Fidelity Pointwise enable the design and optimization of the ship design virtually, although, assuming the real-world operating environment. Marine engineers can also use specialized tools such as the Cadence Fine Marine Solver to calculate the different hydrodynamic and aerodynamic parameters that the marine vessel is exposed to.
The fine meshing and simulation ability of CFD tools can be used to analyze the fluid-structure interaction between the hull and fluid. The resulting value of propulsion, resistance, etc., can be used for hull form optimization, i.e., to reduce drag and improve efficiency through changes in hull form design.