elementGeometryType

The geometry of an element is composed of primitives, i.e. cuboids, cylinders, cones, ellipsoids, tori and multi-segment shapes, and of shapes read from external files. Simple shapes are usually sufficient in design, where the installation space and the mass of the equipment matter more than its detailed form.

Coordinate systems

Each primitive is defined in a coordinate system of its own, described on its page. Its <transformation> rotates and then translates it into the coordinate system of the element; it has no scaling. The <transformation> of the geometry then scales, rotates and translates all primitives together within the element coordinate system (transformationType). Its @refType has no meaning here, since the geometry has no parent other than the element.

Grouping of primitives

The primitives of an element are grouped, not united: overlapping primitives remain separate solids. The volume of the geometry, its centroid and a mass derived from <density> therefore count an overlap once for every primitive that contains it. This is intended; whether and how primitives are united, e.g. by Boolean operations in a CAD kernel, is left to the designer. Where primitives overlap, give the mass by <mass> rather than by <density> (see elementMassType).

Representation

The attribute @representation says what the geometry stands for: the physical shape of the element, which is the default, an envelope around it, or a placeholder (geometryRepresentationType).

A hydraulic accumulator composed of a cylinder and two domes that close it at both ends. Each dome is half an ellipsoid, the half on the side of the positive y-axis given by a revolution angle of π, turned by 90° about the x-axis so that it lies above the cylinder, or by -90° so that it lies below it. The primitives touch without overlapping; the mass is given together with its center of gravity and inertia:

<accumulator uID="element_accumulator">
    <name>Hydraulic accumulator</name>
    <geometry>
        <cylinders>
            <cylinder>
                <radius>0.12</radius>
                <height>0.36</height>
            </cylinder>
        </cylinders>
        <ellipsoids>
            <ellipsoid>
                <radiusX>0.12</radiusX>
                <radiusY>0.08</radiusY>
                <radiusZ>0.12</radiusZ>
                <revolutionAngle>3.141592654</revolutionAngle>
                <transformation>
                    <rotation>
                        <x>90</x>
                        <y>0</y>
                        <z>0</z>
                    </rotation>
                    <translation>
                        <x>0</x>
                        <y>0</y>
                        <z>0.36</z>
                    </translation>
                </transformation>
            </ellipsoid>
            <ellipsoid>
                <radiusX>0.12</radiusX>
                <radiusY>0.08</radiusY>
                <radiusZ>0.12</radiusZ>
                <revolutionAngle>3.141592654</revolutionAngle>
                <transformation>
                    <rotation>
                        <x>-90</x>
                        <y>0</y>
                        <z>0</z>
                    </rotation>
                </transformation>
            </ellipsoid>
        </ellipsoids>
    </geometry>
    <mass>
        <mass>14</mass>
        <location>
            <x>0</x>
            <y>0</y>
            <z>0.180</z>
        </location>
        <massInertia>
            <Jxx>0.2</Jxx>
            <Jyy>0.2</Jyy>
            <Jzz>0.09</Jzz>
        </massInertia>
    </mass>
</accumulator>