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Life cycle stages of a ship hull surface model.


I am often asked about the mathematical model of the surface, and I am more and more convinced that most of the design companies do not pay due attention to this. In this article, I tried to formulate the main stages of working with a mathematical model of the ship's surface. I hope that this article will also be useful for students of shipbuilding and naval architecture faculties of universities.


1. The initial stage - the shape of the hull is determined based on sketches of the General Arrangement (profile, plan, midship - frame) and a close surface prototype, if any. The fastest way to obtain a surface at this stage is to transform the prototype into a General Arrangement drawing. A new surface can be obtained in just an hour, while the body lines drawing will look quite professional. Note that your surfacing tool must support these transform functions. I already wrote about it here. The theoretical drawing and surface model at this stage is used to issue preliminary hull drawings, hydrostatics calculations, refinement of General Arrangement drawing, release of a presentation model to demonstrate the appearance of the vessel to the customer.


2. Stage of preliminary design. After all design tenders are won and a contract is signed, it becomes necessary to refine the surface of the hull in more detail for compliance with the ship's contract specification. As a rule, a lot can change - overall dimensions, displacement, position of the center of gravity, etc. At this stage, higher requirements are placed on the mathematical model of the surface in terms of smoothing quality, the absence of gaps between surface areas and a more accurate modeling of surface details. If you used some primitive ship surface modeling apparatus in the first stage, you will need to convert the preliminary model into another surface modeling program that allows you to model the hull in more detail. This can be avoided by using the same software.



3. Stage of hydrodynamic optimization of the ship's hull surface. More and more companies are now using CFD for hydrodynamic optimization of the ship's hull. This reduces the water resistance of the vessel, increases its efficiency and reduces harmful emissions into the environment. The essence of the optimization process is a consistent local modification of the surface based on the results of the model run in CFD. CFD calculations place special demands on the representation of the surface model and its quality. For the calculation, only the model presented in the form of a “solid body” can be used. Representation in the form of surfaces cannot be used due to the specifics of this calculation. The surface is divided into grids. Moreover, the formed “solid body” should not have gaps. Otherwise, during the calculation process, the hull will fill with water and sink. In this regard, the accuracy of surface model transformation for hydrodynamic calculations should be very high.




I also want to emphasize the second necessary condition, in order to obtain more accurate results of CFD calculations - the surface of the case must be well smoothed. Very often, a poorly smoothed surface leads to the fact that the designer loses confidence in the calculation due to too large errors in the results. Although, in fact, the problem is not in the calculation itself, but in the original surface.

CFD calculation is carried out in several iterations. As a rule, to understand the process of influence of the shape of the body on the resistance, it is necessary to perform 5-6 runs of the model. At the same time, it is important to keep all variants of the hull shape and have a good apparatus for comparing them. This greatly simplifies the analysis of the influence of the hull shape on the water resistance. The hull shape optimization process runs in parallel with the rest of the design work, so when making changes to the hull shape, other design parameters such as center of gravity, stability, and compliance with internal volume restrictions must be taken into account. More information on hydrodynamic optimization can be found here.



4 Final smoothing of the hull surface for production. After most of the design work is completed, the final smoothed surface of the ship's hull is produced. When smoothing, it is necessary to take into account the technological features of the hull, the capabilities of the shipyard, and many other details. At this stage, not only the hull is modeled, but also all the internal curved surfaces of the hull, superstructures, deckhouses and masts. I often come across the fact that when modeling surfaces, different software products are used simultaneously. As a result, the model is not coherent. With this approach, it is very difficult to trace changes in the shape of the hull surfaces as a result of revisions. At this stage, when the ship's hull is embodied in metal, this is especially important. I already wrote about the optimal structure of the mathematical model of the project here. The importance of maintaining a single integral hull model is also relevant at the next stage of the surface life cycle.



5. The stage of archiving the model. Although the ship has already been built and the project has been completed, the mathematical model of the surface should be kept in case of ship modernization and for use as a prototype for new projects. Having a library of ship hull surfaces saves a lot of time and money in the initial stages of designing a new ship. The results of previous design work are of great help in the design of new ships. In fact, the surface model, together with all calculations, is a significant part of the company's intellectual property.


Summarizing all of the above, I would like to draw the attention of everyone involved in the design process to the importance of the correct organization of work and information flows when modeling the ship's surface.

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