Feature 3 | CAD/CAM UPDATE New solution for hull surface modelling


An innovative patchwise surface generation tool allows advanced hulls to be modelled with speed and ease, according to its developer.


G


RC Ltd has been developing what it says is a powerful new tool for the creation of high quality surfaces and


hullforms. Paramarine is an integrated product for naval architecture design and analysis, and is reckoned to be the only product that deals specifically with surface ship and submarine design in an integrated fashion through a single user interface. Paramarine capabilities include early


stage design, hullform generation, design for production, stability and hydrostatics, damage stability, structural definition, ultimate strength, radar cross section, blast and fragmentation, powering and endurance, manoeuvring, and sea-keeping. The development of the advanced hull


generation capability is regarded as a key component of the early stage design process and needs to provide a rapid, intuitive, and parametric capability, such that multiple hullform concepts can be designed, assessed, and optimised within the soſtware. Designers need a tool that provides the


maximum amount of control over the surface generation coupled with a high quality output, as the surfaces and corresponding solids will be used for the various analyses available within Paramarine. Tere is, thus a clear need to enable hulls or


other complex surface shapes, such as curved superstructures and submarine casings, to be defined rapidly, and then parametrically altered if necessary without having to be completely re-worked. Tat means an intuitive user interface, allowing easy control over the definition of the curves.


The Hull Generator Te solution developed by GRC to satisfy these requirements is known as Hull Generator, which will be presented first at this year’s CompIT symposium in Liege (Belgium) at the end of April. Te tool will be available in the next release of Paramarine due in the early summer. Hull Generator incorporates functionality


known as ‘X-Topology’ which refers to the process of forming a topological network from


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Figure 1: Exemplary parametric Hull Generator surface.


the curves supplied and using this topology for infer-boundary conditions at the edges of the surface patches formed for the multi-patch hull. From the earliest stages of development,


users’ views on the proposed functionality have been sought, paying particular attention to UK shipbuilders and other naval architecture consultants. Naturally, not all users require the same things in a hull generation system, but what became clear during this process was that users need to define the hull in terms of 2D and 3D curves representing particular hull features, for example, flat of side, flat of keel, waterline, and knuckle lines. Secondary curves can then be developed (mainly in 2D) to give key section lines, buttock lines, and waterlines. Further key user requirements were


identified from workshops and discussions with users: ease of use, speed of use, flexibility, audit trail, diagnostics, ability to import images such as bitmaps for rapid development of curves, and compatibility with external soſtware. Users then expect the hull


generation system to calculate the shapes of the 3D surface patches formed in between the curves, with slope and curvature continuity where expected. Tis is a very tall order for a patchwise hull generation system but one which Hull Generator has achieved. Te user defines curves from a high-level


perspective. Strategic points are placed and the corresponding features of the curve are described in terms familiar to the user. Te user does not need to be an expert in NURBS mathematics and is free to concentrate on what hull shape and features are required, rather than how it should be achieved in the soſtware. Te example in Figure 1 shows the graphical


display of the port side of a hull designed in Hull Generator. Te user, generally, will firstly define the edges of the surface he/she is trying to create: in this case the deck edge, the profile, and transom curve define the boundaries of the surface. Te user inserts these curves graphically and defines the way they are connected together by snapping points together or by snapping points along


The Naval Architect April 2008


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