﻿ Shapes

Shapes

Shapes are simple three-dimensional geometric objects that may be fixed in place or connected to other objects. Each has a specific type:

• Elastic solids are used to model physical obstacles
• Trapped water shapes are used to model moonpools or other areas where fluid motion is suppressed
• Drawing shapes have no physical effect on the model and are intended for drawing purposes only
• Labels have no physical effect, but define arbitrary text to be drawn on the 3D view

In addition, each has a specific geometric shape, one of block, cylinder, curved plate, and plane.

 Figure: Examples of block, cylinder and curved plate shapes

These two fundamental properties, type and shape, may be combined (with the exception of labels, which are shapeless) to represent a variety of objects. For example, an elastic solid with a curved plate shape can be used to model a bellmouth, or a cylindrical trapped water shape can represent a moonpool.

Shape types

Elastic solids

An elastic solid represents a physical barrier to lines, 3D buoys, and 6D buoys; it has no effect at all on other objects. It is made of a material of a specified stiffness which, when contact occurs, resists penetration and, through friction coefficients, generates friction. Full details of these calculations are given under the shape theory topic.

Note, however, that elastic solids are intended only for modelling the overall limitation on movement that a physical barrier presents; they are not designed to model an object's interaction with the barrier in detail. The calculations of, for example, the contact area and penetration depth are simplistic, and do not allow for the detailed geometric shape of the object.

Lines only interact with elastic solids through their nodes, so it is possible for an elastic solid smaller than the line segment length to fall between adjacent nodes without making contact – the line appears to simply pass through the solid unhindered. The line segment length should be therefore be small compared to the dimensions of any elastic solid with which the line may make contact.

Trapped water

Trapped water can be used to model hydrodynamic shielding, such as inside a spar, where wave and current effects are suppressed.

Inside a trapped water shape, the fluid motion is calculated as if the fluid were moving with the shape. So if the trapped water shape is fixed, then no fluid motion occurs in the shape – representing a breakwater, for instance. But if the shape is connected to a moving vessel, say, then the trapped water moves with the vessel – this effect could be used to model a moonpool.

 Notes: Objects are not affected by any trapped water shapes which are connected to themselves. If they were, this would set up an undesirable feedback loop (consider a buoy, part of which is in trapped water: the buoy motion determines the position of the shape, but the shape affects the buoy motion…). If a trapped water shape is attached to a line, the single line node where the attachment is made cannot be shielded by the trapped water, but the rest of the nodes in that line will be shielded when they are within the shape. If a trapped water shape is surface-piercing, the wave surface appears within the shape unaltered.

Drawing shapes

Drawing shapes have no physical effect on the model. They can be used to draw objects of interest and do not interact with other objects.

Label shapes

Label shapes have no physical effect on the model, and the geometric shape is suppressed. They are used to draw arbitrary text labels on the 3D view.

 Notes: Label shapes is something of a misnomer since they have no shape. Whilst this is potentially confusing, we took the decision to include this functionality in the shape object because it is the object most commonly used purely for visualisation. Text labels are not drawn for shaded graphics views.