Shape Maker in ship design.
In this article, I would like to describe the technological process of creating the surface of a ship and the place of the Shape Maker in this process.
Any project of any type of ship at the earliest stage of development must have a lines drawing of the ship's hull. Of course, any project relies on previous experience and your new project will look like some kind of prototype. I would not like to dwell in this article on how to select the most suitable prototype, as well as all other parameters of the future vessel. The designer knows this like no one else, and it is on his technical solutions that the project is built. As a rule, at the stage of development of a lines drawing, all the main technical decisions have already been made. At least the main dimensions, the bilge radius, the shape of the stems, the type of stern and stem, the contours of the decks and the design waterline, and the displacement should already be known.
The most useful information for the design of the surface of the ship's hull is presented in the general arrangement drawing. The profile of the ship, the outline of the midship frame, the decks are usually presented on this drawing and are the initial information for surface design. As a rule, the general arrangement drawing shows the position of the flat side and flat bottom line.
The general arrangement drawing can be loaded into the Shape Maker. To do this, do the following:
- save the required views in separate DXF files,
- Align the origin of the drawing coordinate system with the origin of the AutoCAD coordinate system,
- clean up unnecessary information that is not needed for surface design, such as texts, hatching, clouds, etc.,
- explode blocks,
- save the DXF file to the earliest possible version, preferably R12. In this case, all elements of the drawing are converted into the most primitive ones, which are loaded into the Shape Maker seamless. Note that the current version of DXF file import does not support ellipses.
To import views into Shape Maker, it is better to create a structure from the following blocks and import each view into the corresponding block. This facilitates the process of importing and visualizing information. At any time, any of the blocks can be turned on or off.
- Template
-- Profile
-- Plan
-- Midship
The import process is as follows:
- the current block is selected, for example Profile,
- the corresponding DXF file is imported into the current block.
All views from the GA drawing are represented on the XY plane and will be imported into the Shape Maker accordingly on the same plane. To arrange them in the appropriate planes, you can use the rotation and movement of the blocks. Use block selection by block element to rearrange projections.
Now that all the views are loaded into the Shape Maker, we need to set up a grid of frames, waterlines, and buttocks. Shape Maker allows you to define areas with constant spacing in all three coordinates. Additional sections are highlighted in yellow during output. As additional sections, you can set stations, constructive waterline, decks. The grid can be changed at any time. Visualization of surface sections is performed in accordance with the section planes specified by the grid. At this point, the preliminary preparation process can be considered completed.
Now the fun begins.We are starting to design the surface of our vessel.To do this, we create the following block structure:
HULL 0
- ForeShip
- AftShip
-Midship
These blocks will contain the first version of our surface.Select the ForeShip block as current.In Shape Maker, the concept of current block means that all newly created elements will belong to this block.
In the process of setting the boundary lines of surface sections, it is convenient to use object snapping to template points. In this case, I strongly recommend not to use topological binding to template points, but to use geometric binding. You can learn more about topology in Shape Maker here. In the case of a topological snap, the points will belong to the template block and may not be editable when the template is turned off. It is also desirable to use a color that is different from the color of the template elements. The template preparation video shows this process in real time.
Our task is to model the surface patches that describe the ship's hull. The only way Shape Maker uses it is to define a surface area based on a set of interrelated curves. These curves will be the boundaries of our surface area. So let's start with defining boundary curves. Shape Maker allows you to create surface areas based on 2, 3 and 4 boundary curves. The most common combination of boundary lines in our case is:
- bilge radius line on the border of the cylindrical insert or on the midship frame,
- flat bottom line,
- stem line,
- knuckle line, turning into a flat side line.
Therefore, we first set the contour of the boundary lines of our future surface patch. The very first approximation of a line between two endpoints in Shape Maker is a straight line. Therefore, first, in fact, you need to set the corner points of our future surface, connected by straight lines. Point coordinates can be set using geometric references or using the coordinate input line from the keyboard. Each new input line is topologically connected to the previous one through a common point. To create a surface, when entering the last point of the contour, it is necessary to topologically connect it with the first point of our contour. Without this, it will not be possible to set a surface area. More information about defining a surface can be found here.
Now we have a contour, which so far does not at all remind us of anything from our future ship, but the corner points of our future surface are already in place. You can check this by moving from projection to projection or in 3D views.
Let's try to shape our lines. To do this, just click on one of the lines with the cursor and change the position of the points of the control polygon that appears. More information about lines in Shape Maker can be found here.
Let me remind you that the control polygon of the original line has only two control points. The slope angles at the end points of the curve are determined by the corresponding control polygon vector. Left click on an intermediate point of the control polygon, move it to a new position and click again. As you move the control point, you will see how the shape of the curve changes. Control point coordinates can also be changed from the keyboard. To do this, without releasing the point, click the cursor in the coordinate input window and change them. The input focus automatically switches to coordinate editing mode when you press the left arrow or right arrow on the keyboard. Editing coordinates is completed by pressing Enter on the keyboard. You can interrupt the process of changing the position of the control point by pressing ESC or the right mouse button.
Do not think that the two internal points of the control polygon will allow you to accurately determine the desired shape of the curve. At this stage, we restrict ourselves to defining the tangents at the beginning and end of each boundary curve. Note that many boundary curves require horizontal or vertical tangents at the endpoints. So, at the point of contact with the cylindrical insert, the lines of the flat bottom and flat side should have horizontal tangents. The same applies to the stem line at the point of contact with the main plane. To set orthogonal tangents - vertical or horizontal, just click on the line of the control polygon that defines this tangent, while holding down the Ctrl button. More information about line editing can be found here.
Increase the number of points in the control polygon. To do this, click on the line connecting the internal points of the control polygon with the Ctrl button pressed simultaneously. The extra control point will give us more options to change the shape of the curves. Increasing the number of control points does not change the shape of the curve. This property allows you to modify curves locally. When increasing the number of edge curve control points, one simple rule to keep in mind in Shape Maker is that the number of surface control points depends on the number of edge curve control points. This is described in more detail here. I recommend gradually increasing the number of points. This will significantly reduce the complexity of the surface formation process.
By changing the position of the points of the control polyhedron of the surface, we achieve the required shape of the hull. If you have used the general arrangement drawings as input, the outlines of the deck lines can be used as reference points in the initial stages. I only recommend in this case to set the position of the deck lines as additional sections along the waterlines. This will greatly simplify the work of bringing the surface closer to the lines of the decks. Further actions to smooth the surface are well described here.
If you have a surface model of a vessel that is similar in shape to the design, you can use this model and transform it to a new project. This is the fastest and most efficient way to get a first approximation of the surface of a new project. This process is well shown on this video.
So, we have the first approximation of the surface of the new ship's hull. What information can we get from our surface model?
- First of all, this is of course a lines drawing. The lines drawing is one of the main drawings used at all stages of ship design. In Shape Maker, the lines drawing is generated automatically based on the drawing's grid. This process is described in more detail here.
- In addition to the lines drawing, Shape Maker allows you to generate many different files that can be used when designing a ship. The list of output information can be found here.
- The main hydrostatics characteristics of the hull, such as displacement, position of the center of buoyancy, wetted surface area, metacenter height and others, can be obtained using the built-in hydrostatics calculations. In addition, you can get section area curve(SAC). This curve is widely used in hydrodynamic hull optimization.
- In Shape Maker, in addition to the surface of the hull, you can model almost any appendages, internal surfaces of the hull, surfaces of superstructures and weelhouses. This makes it possible to check our surface for the possibility of placing equipment inside the hull. Thrusters for fishing boats, for example, are often problematic. All of them are easy to detect in the modeling process.
The design of a ship is a cyclical process, where at each new stage of the project it often becomes necessary to change the shape of the hull. In Shape Maker, you can save all versions of the hull surface. This gives a complete overview of the changes at all stages of the project. In this case, any of the versions of the surface can be used to create models of a new project. To do this, just copy the version of the package to a new project.
The hull surface model is also used to calculate the hydrodynamic characteristics of the vessel, such as drag, roll, and sea keeping. If any of these characteristics do not meet the requirements of the classification society or contract, the surface model must also be modified.
This is especially important for optimizing the resistance of the ship's hull. Undoubtedly, the water resistance of the vessel is one of the most important parameters that determine the efficiency of the vessel as a whole. The reduction in resistance results in a reduction in operating costs and a reduction in harmful emissions into the environment. This optimization is itself a cyclical process. Based on the surface model, the process of water flow around the body and, accordingly, the resistance is calculated. The output information after such a calculation can be loaded into the Shape Maker and rendered. Based on the study of the flow pattern around the body, changes are made to the shape of the surface and the process is started again. As a rule, after five or six iterations, the shape of the hull with optimal resistance is determined. All variants of the hull shape made during the optimization process are also saved in the project database and can be used in new developments. More information about hull optimization can be found here.