Splitting into surface patches.
To say that correctly dividing the ship's surface into patches is important is to say almost nothing. Correct surface subdivision is the key to building a correct model and sometimes this is far from a trivial task. Fortunately, on ships of the same type, you can use a successful surface division from a previous project. In this article, I will try to present typical hull surface subdivisions for different types of ships.
Basic rules and requirements for surface division:
- always set the design lines as boundary lines of surface patches, even if these lines are not knackle lines. This will allow you to more accurately determine the shape of the design lines. So the lines of the flat side and flat bottom should be set.
- try to describe curved surfaces with one patch. A smooth joint of two curved surface patches is possible, but it does not always look aesthetically pleasing. Within the same surface patch, the condition of smoothness of not only the tangents to the lines, but also the curvature is satisfied.
- define the patches of the parallel midbody, if possible. The surface of the bilge radius should be presented as a separate surface patch.
- make flat patches of the hull as separate surfaces wherever possible. In order to make a flat patch on the surface, it is enough to set the area of control points on the required plane. With this approach, it is very difficult to control the shape of the transition line from the plane to the curved surface. It is much easier if, for example, the line of the flat side is the boundary of the flat and curved surface.
Fig. 1 An example of dividing the fore ship of the ship's hull into a curved surface of the hull, a flat surface of the bottom and a cylindrical surface of the side.
- avoid sharp corners and diamond-shaped sections of the surface. The location of the points of the control polyhedron of such a surface will not allow you to get a high-quality shape.
- try, where possible, to set the appendages parts as separate surfaces and intersect them with the surface of the hull. Avoid possible singularities, such as the intersection of two merging surfaces. The intersection line of such surfaces may have an unpredictable shape.
- although triangular surface areas are supported by most systems, when designing, it is better to use flat triangular areas, cylindrical or conical areas, or areas with minimal surface curvature.
- when creating a model, it is necessary to take into account the possibility of subsequent changes or use in subsequent projects. A model that can be easily modified can save a lot of time when making changes.
Splitting the hull surface of a twin-screw vessel with a stern skeg into sections.
An example of a typical splitting of a single-screw vessel with a stern skeg and a parallel midbody is shown in Fig. 2
The bow end is represented by three surface patches. The curved surface of the hull itself is framed by a triangular patch of the flat bottom and a quadrangular cylindrical patch of the flat side surface, which turns into the vertical part of the bulb above the knuckle line. This is a fairly typical splitting scheme for the fore shi. In this case, the presence or absence of a bulbous bow on the vessel does not play a significant role. In any case, there will be only one curved surface.
The parallel midbody is also represented by three surface patches, which are, as it were, a continuation of the surfaces of the fore ship. The sides and bottom surfaces are flat, respectively, and the bilge surface is cylindrical.
The surfaces of the aft ship can be divided into two groups: the surfaces of the main body and the surfaces of the skeg.
Subdivision of the fishing vessel hull surface into sections.
Fishing vessels have some features that must be taken into account when subdividing the surface into patches. Deadrise and construction trim somewhat complicate the definition of the surface. Let's consider two of the most widely used subdivision options.
One of them is shown in Fig. 3. In this option, the bow surface is defined without separating the flat-keeled bottom section. This presents additional complications when it is necessary to define a flat surface section as part of the bow end. The advantage of this subdivision option is a solid section of the stern surface, while maintaining the continuous smoothness of the surface.
Fig. 3 An example of subdividing the surface of a fishing vessel into patches without separating the flat bottom patch in the fore ship.
Another option for subdividing the surface is shown in Fig. 4 An example of subdividing the surface taking into account the flat-keeled bottom in the bow. Fig. 30. The flat-keeled bottom in the fore ship is separated into a separate surface patch. This makes it easy to control the shape of the flat bottom line. In this case, we have to divide the stern surface into two sections. Only smoothness along the first derivative will be ensured along the junction line of the stern sections of the surface. Due to the fact that the stern surface has a rather simple shape, I prefer to use this version of division. Note that in Fig. 4, a section of the parallel midbody of the surface is highlighted. This is sometimes useful if you plan to lengthen the hull in the area of the parallel midship in the future.
Fig. 4 An example of dividing the surface taking into account the flat-keeled bottom in the bow.
A feature of this method of specifying the fore ship is that the line of the flat-keeled bottom in the bow must lie in the plane of the general position formed by the keel inclination line and the bottom inclination line on the midship - frame - Fig. 5. The bottom line is also the lower boundary line of the curved bow surface. Therefore, it is convenient to create the bottom plane as a template and project the bottom line onto this plane after editing. Such a plane is also especially convenient for controlling the entry of frames into a flat bottom.
Fig. 5 Example of a flat-keeled bottom line (shown in red) and a general position plane.
It is important to note another feature when designing the aft ship of a fishing vessel. The main surface of the stern is passed over the centerline plane at the point of contact of the stern skeg and, subsequently, is cut off by a surface line passing in the centerline plane. That is, the stern part of the centerline buttock after the skeg is a surface line on the main surface of the stern. The skeg profile line in this case is hung on the skeg knuckle line. At the same time, the break line serves as the boundary of the main surface of the stern. For ease of skeg modeling, the upper point of the skeg profile should come strictly to the node on the knuckle line. This will provide a predictable number of control points on the skeg surface patch and facilitate the process of giving the skeg the required shape.
Fig. 6 Section of the stern surface, skipped beyond the diametrical plane. Trimming of surfaces and lines is disabled.
Splitting the aft ship of a single-screw vessel with a skeg integrated into the hull.
The aft ship of a single-screw vessel with a skeg smoothly transitioning into the hull is one of the most difficult tasks for surface smoothing. Fig. 7 shows an example of such an end. Due to the limitation on the number of boundary lines of the surface area, in this case the flat bottom line and the skeg profile line are formed as one boundary line of the main surface area of the stern. The aft boundary line is a pseudo-transom line, the flat side line and the chine line are defined as for a normal section of the aft surface. Subsequently, the surface is trimmed by the transom surface. When modeling such an end, I recommend starting with a minimum number of control points and increasing their number as the surface is formed. The number of control points for describing such a surface can ultimately be quite large.
Fig.7. An example of a single-screw vessel with a skeg smoothly transitioning into the hull. The main surface is shown without trimming.
Fig. 8 The final version of the stern with the transom surface trimmed.
Breaking down the aft end of a twin-screw vessel with two skegs.
The aft ship of a twin-screw vessel with two skegs is also quite common in shipbuilding.
In this case, the main aft surface is made separately from the skeg and subsequently intersects with the skeg surface. This gives quite a lot of freedom in changing the position of the skeg when designing the vessel. When using this model, it is important to smooth the surfaces well at the intersection of the skeg and the main hull. Otherwise, the intersection line may not look smooth enough.
Breaking down the aft end of a twin-screw vessel with two skegs.
Fig. 9. An example of the aft end of a vessel with two skegs.
I would like to once again emphasize the importance of correctly dividing surfaces into sections and I hope that this article will help you in the initial stages of learning the program.
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