Free Side Syntax

<boundary_1> and <boundary> have the same definition as in the normal BOUNDARY syntax. <boundary_n> is the boundary which is 'free'. <boundary_n-1> and <boundary_n+1> are the boundaries before and after the 'free' boundary, respectively. The free side may be quite empty.

<boundary_n> may be the first boundary and, in this case, <boundary_n-1> is the last boundary.

<boundary_n> may as well be the last boundary and, in this case, <boundary_n+1> is the first boundary of the panel.

<boundary_n-1>::= <boundary_n+1>::=

<boundary_1>|<boundary>, LENGTH=<length_of_limit>

<boundary_1> may occur only as the first boundary.

<length_of_limit>::= <length>|(H+|-<dist>)

<length>::= <dist>::= <number>

In case the boundary is of type <profile_crossection> (see Syntax Normal), H is the height of an intersecting profile section, defining the limit in question. See the image below.

In case a boundary of type <overlap_profile_end> (see Syntax Normal), H is the length of the contour between the two end points A and B in the image below.

H is the length of the boldly marked parts of the image.

<boundary n>::=

<preliminary_boundary>
[,FREE]
[,M1=<m1>]
[,M2=<m2>]

<preliminary_boundary>::= <boundary>

The meaning of <l1>, <v1> will be explained in the images and the remarks below.

1.

The keyword FREE is used to identify the free side. Normally, Hull Modelling is able to evaluate that from the rest of the input, but in the following case ambiguity will prevail if FREE is not given.

• there are four boundaries

• the free side looks like an ordinary boundary (that means, it is not empty and has no parameters).

Then boundaries 3 and 4 will not be selected as the free side unless FREE is given. FREE can be given also in the cases when it is redundant.

2.

The boundaries must form a preliminary closed contour according to the same rules as for Normal Syntax. If the boundaries except <boundary_n> fulfill this requirement, then <preliminary_boundary> may be missing, as in the image below, where the boundaries 1, 2, 4 and 5 form a closed preliminary contour. No <preliminary_boundary> need be given for boundary 3 (= <boundary_n>).

(The figures are boundary numbers.)

If this requirement is not met as in the image below, then a <preliminary_boundary> must be given. Here, <boundary_n> is boundary 2 and the boundaries 1 and 3 do not form a closed contour. Thus a <preliminary_boundary> must be defined for boundary 2.

3.

The preliminary contour created in this way will then be modified to the final contour in steps as follows:

1. <boundary_n-1> will be shortened to the length <length_of_limit> (or possibly extended), counted from its starting point.

2. <boundary_n+1> will be shortened to the length <length_of_limit> (or possibly extended), counted from its ending point.

   If the original length of the boundary is less than the one demanded, then the contour will be extended along its tangent in the concerned end point.

3. So far, the end points of the 'free' boundary <boundary_n> are defined. Its detailed shape is controlled by the parameters given in <boundary_n> as illustrated below. There are two cases.

Case A

The free boundary has two toes connected with a line segment. (Keywords R1 and R2 are used.)

Parameters at start of free side:

Parameters at end of free side:

The parameters define two 'toes', one at each end of the free side.

<m1>/
<m2>

is the height (or length) of the toe in a direction perpendicular to <boundary_n-1>(/<boundary_n+1>). May be missing.

<r1>/
<r2>

is the radius of the arc being part of the toe. May be missing.

<v1>

is the inclination in the positive direction of arc 1 relative to the preceding segment, measured in the counter-clockwise direction.

Default values:

m1 = 0

v1 = 80

m1 > 0

v1 = 0

Note: If v1=0, then m1 should be considered a toe length rather than a toe height.

<v2>

is the inclination in the negative direction of arc 2 relative to the following segment, measured in the clockwise direction.

Default values:

m2 = 0 :

v2 = 80

m2 > 0 :

v2 = 0

Case B

The free boundary has two 'toes' connected by one radius. (Keyword R is used.)

Two sub-cases may occur:

I.

<t1> and <t2> are omitted.

This means that the two 'toes' are connected by the arc with radius <R>.

Free side, consisting of toes and one arc:

II

<t1> and <t2> are both given.

Then an arc with radius <R> will be inserted as a fillet between two lines from the toes. The deviation angles of these lines relative to adjoining segments will be <t1>(=80) and <t2>(=85), respectively. See the image below.

4.

The following procedure is recommended when generating a panel with a free side:

4. Decide how many boundaries the panel finally will have. Write BOUNDARY and one new slash on a new line each for the boundaries 2, 3, giving:

   BOU,

     /

     /

     / ...

     ;

5. Decide the number of the free boundary and write down the other boundaries. It is never wrong to add FREE to the free side even if it is not required in most cases.

   BOU, 'A'

     / 'B'

     / FREE    ('free side')

     / 'C'

     / ...

     ;

6. Examine if the boundaries, so far defined, form a closed contour. If not, add a rough preliminary boundary along the free side, closing the contour.

7. Add 'length_of_limit' along the surrounding limits, giving:

   BOU, 'A'

     / 'B', LEN = ...

     /   ('free side')

     / 'C', LEN = ...

     / ...

     ;

8. Finally, add toe heights, radii, for the free side giving:

   BOU, 'A'

     / 'B', LEN = ...

     / M1 = ... , R1 = ...

     / 'C', LEN = ...

     / ...

  ;

Note: The free side may be quite empty (if it has no toes, for instance).