&CELL: SOLIDS: HOLE

CENTRE

The location of the point that is on the central axis of the hole, half-way between the 2 planes of the box perpendicular to the central axis of the hole.

[No default.]

radius

The radius of the hole as measured at the "lower" and at the "upper" surface of the box. If these radii are the same, then only one of them needs to be entered.

The decision whether a particle is inside or outside the cylindric part of the hole is made assuming a genuine cylinder. For plotting and neBEM field calculations however, a polygonal approximation is made and the precise interpretation of the radius is influenced by the MEAN-RADII and OUTER-RADII options.

[No default.]

OUTER-RADII

By default, the polygonal hole is inscribed in a circle of the specified radius.

MEAN-RADII

If this option is specified, then the radius will be interpreted as the average radius of the polygon that approximates the cylinder. The radius at the vertices will be larger than the smallest enveloping circle by a factor:

2/(1 + arcsinh(tan(\&alpha;) cos(\&alpha;) / tan(\&alpha;)))

where

\&alpha; = 1/4 \&pi; / (N-1)

If you insert a precisely fitting cylinder in the hole, then you should use the same option for the cylinder.

[This is not default.]

HALF-LENGTHS

Half the overall dimensions of the box.

[No default.]

DIRECTION

The direction vector of the central axis of the hole.

The normalisation of the vector is not used. Zero-norm vectors are not acceptable.

[By default, the central axis is aligned with the z-axis.]

CHARGE

Charge applied to the surfaces of the hole.

The charge is added to the surface charges needed to satisfy the boundary conditions. The hole can either be a dielectric or a conductor.

In the process of being implemented - initially, the charge is equally distributed over all surfaces, selection of surface panels is planned to be added later.

Specifying this option implies the use of neBEM to solve the field.

VOLTAGE

Voltage of the hole, which is assumed to be conducting.

Specifying this option implies the use of neBEM to solve the field.

FLOATING-CONDUCTOR

The hole will assume a uniform voltage common on all its surface panels.

In the process of being implemented.

Specifying this option implies the use of neBEM to solve the field.

EPSILON

Dielectric constant of the hole relative to vacuum.

Specifying this option implies the use of neBEM to solve the field.

material

Specifies whether the hole is made of conducting or from dielectric material. To differentiate the solids in drawings, one has the option to choose between various representations:

Type	Representation	Notes
`CONDUCTOR`	`CONDUCTORS-1`	Equivalent to CONDUCTOR-1
`CONDUCTOR-1`	`CONDUCTORS-1`	-
`CONDUCTOR-2`	`CONDUCTORS-2`	-
`CONDUCTOR-3`	`CONDUCTORS-3`	-
`DIELECTRICUM`	`DIELECTRICA-1`	Equivalent to DIELECTRICUM-1
`DIELECTRICUM-1`	`DIELECTRICA-1`	-
`DIELECTRICUM-2`	`DIELECTRICA-2`	-
`DIELECTRICUM-3`	`DIELECTRICA-3`	-

[Default: CONDUCTOR]

N

The hole is drawn as an outer box and an inner hollow cylinder. The choice of n has no impact on the box. The inner cylinder is drawn as a polygon with a finite number of panels. The number of corners of this polygon equals 4(n-1). Thus, n=2 will produce a square, n=3 an octagon.

The interpretation of n is the same for holes and cylinders. Cylinders with a given n will precisely fit in holes with the same n, provided the radii and axes match.

Drift line termination assumes a perfect cylinder, the choice of n therefore has no importance for this purpose. However, the number of surface panels passed on to neBEM field calculations rises with n and the visual quality of 3D views improves with n.

[By default, N is chosen in function of the size occupied by the cylinder in the drawing. N must be larger than 1.]

label

A one character identification of the solid.

This label serves the same purpose as the wire label for wires, namely the selection of the solid as a place where signals can be measured, around which isochrons are drawn etc.

[By default, no label is assigned.]

discretisation

The approximate linear size of the elements you would like neBEM to use when discretising.

Garfield generates, for each solid, a set of panels that together cover the faces. These panels, arbitrary convex polygons, are sub-divided when isolating contact areas between solids and also in order to comply with the neBEM requirement that it be given only rectangles and right-angled triangles. The triangles and rectangles handed to neBEM are called "primitives".

For reasons of accuracy neBEM as a rule sub-divides the primitives into "elements", in a process called "discretisation". The sub-divisions of the primitives are called "elements".

Discretisation will perhaps eventually be automated, but for the time being this remains the responsability of the user. In neBEM, the level of discretisation requested is described by 2 integers: the number of elements that is to be generated along each of 2 sides adjacent to a right angle. Since the shape, orientation and size of the primitives are non-trivial to predict, the level of discretisation is specified on the Garfield side as the desired length of the sides of the elements.

The designation of the surfaces is as follows:

front: the +x face of the box;
back: the -x face of the box;
right: the +y face of the box;
left: the -y face of the box;
top: the +z face of the box;
bottom: the -z face of the box;
hole or cylinder: the surface of the hole.

All references to coordinates concern the situation before the solid is rotated in place.

The discretisation lengths can be set in several ways, see Example\ 4 for the SOLIDS command:

by setting a default discretisation length to be used for all solids, by means of the TARGET-ELEMENT-SIZE keyword of a NEBEM command issued before the SOLIDS command;
collectively for all faces of a single solid, e.g. DISCRETISATION=0.1, this overrides the default used for all solids;
individually for one or more faces of the solid, e.g. TOP-DISCRETISATION=0.2, this overrides any previous collective setting;
by setting the discretisation length of a face to AUTOMATIC; if this face is in partial contact, then the discretisation length of the other face will be used, if it has been set; if not, and also in the absence of contact, the TARGET-ELEMENT-SIZE will be used that is in effect when leaving the cell section.

Discretisation lengths have to be given in cm. [Default: the TARGET-ELEMENT-SIZE that is in effect at the time the solids are read.]

Go to the top level, to &CELL, to SOLIDS, to HOLE, to the topic index, to the table of contents, or to the full text.

Formatted on 21/01/18 at 16:55.