Card 9 - XCIRC Circular Element Definition

KODE

KODE is the code XCIRC (or 17)

N1

N1 is an element number, or a group name.

T1

T1 is another element number, or 0 if N1 is a group name.

T2

T2 is a node number.

T3

T3 is another node number.

Notes

This card defines Card 5 elements N1 through T1 to be circular elements whose central axis runs through nodes T2 and T3.

Conductive conductances for circular elements are calculated assuming temperature gradients are logarithmic in the radial direction and linear in the tangential direction. As a special case, if a node of a circular element falls on the central axis, the radial temperature gradient in the element is assumed to be linear in order to avoid a singularity.

You can use circular elements to efficiently model circular geometries such as thick-walled pipes. For example, to accurately describe the surface of a cylinder of unit radius with non-circular elements, you need at least 8 tangential elements. With circular elements, you can accurately model the cylinder with as few as 3 tangential elements.

Lump mass and beam elements are not considered to be circular elements.

For view factor calculations performed by the VUFAC module, each circular element is subdivided into a number of flat elements such that the angle subtended by an edge of a flat element does not exceed 45 degrees. If, however, an edge of a circular element exceeds 135 degrees, that edge is subdivided into three equiangular line segments. View factors and thermal couplings are calculated for these flat elements separately, and are then summed to yield the view factor and thermal coupling of the circular element.

It is important to remember that view factor calculations assume uniform illumination over the element. If the circular element subtends too large an angle, this condition may not be fulfilled, and inaccurate results are obtained.

Circular elements may not be defined as orthotropic elements.

It is highly recommended that circular elements have shapes that have edges along the radial and tangential directions.

Circular elements may not be specified with XCIRC Cards for an axisymmetric model.