SuperNEC
SIG
GUI Manual
Version 0.10
Document
Status: Beta
SuperNEC
SIG
GUI Manual
Version 0.10
Document
Status: Beta
Table of Contents
1.1 Structure interpolation and
segmentation (SIG) approach
3 Performing basic SIG
functions using the Interface
3.1 Opening and Saving projects
3.2.5 Lines
from Workspace Variables
3.3 Selecting and unselecting lines
3.5 Adding, deleting, modifying and
changing between Cross-Sections
3.5.1 Adding
New Cross-Sections
3.5.2 Deleting
current Cross-sections
3.5.3 Modifying
Cross-Section z-values
3.5.4 Changing
between Cross-Sections
3.8.4 Editing
the Number of Points Making up a line.
3.8.7 Reflecting/flipping
lines
3.9 Sending Curve coordinates to
workspace variable
Complex structures
such as, aircraft, ships and motor vehicles etc can be accurately modelled as a
mesh of MoM (Method of Moment) wire segments, for simulation in SuperNEC. For the purpose of easily and quickly
creating these complex wire grid models, the SIG (Structure Interpolation and
Gridding) program was developed.
This manual will
start off by introducing the Structure Interpolation and Gridding (SIG) approach
and method of operation, after which the SIG GUI (Graphical User Interface) controls
and features will be presented. This document will end off by investigating two
examples, which will familiarise the user with SIG and the GUI controls.
SIG is a simple but powerful program which captures and
interpolates three dimensional data and forms a wire grid representation of the
surface which it outputs in a form which can be imported into SuperNEC. A
graphical interface (SIG GUI) has now been added to make SIG even more powerful
and easier to use than before. An example of the operation of the SIG package
is provided in section 7, but the essential operations are summarized below:
·
The user determines which cross-sections
will be used to define the structure for the purposes of the simulation.
Cross-sections are ideally chosen at points of abrupt change along the structure.
Each cross-section is divided into curves to which numerical tags are assigned
for identification of related curves in consecutive cross-sections. These
tagged curves enable the user to model the full structure by introducing and
terminating appendages such as wings, wires emanating from the fuselage,
canopies and the like. Example 1 below illustrates how this is achieved).
·
Each user-defined curve is composed of
discretized points, these points are automatically created by the SIG GUI when
user curves are drawn. The number of points used to represent each user curve
can be set to achieve the level of smoothness required.
·
In addition to the functions described
above the user can also:
Request a
log-file giving all the augmented section information, junction information,
warning and error messages, as well as grid geometry statistics. Grid geometry
statistics include the number of segments, average, longest and shortest
segment lengths as well as the total wire surface area of segments *(This
feature is not implemented in this version of the SIG GUI).
Write out the augmented structure
in the format of a SIG input file (.grd file). This is a particularly useful
feature should the user want to modify some of the computer generated
cross-sections. The edited file can then be resubmitted to SIG to be segmented.
Export curves to Matlab® workspace variables for editing
purposes and/or import new/edit existing curves from Matlab® variables.
Select to view 3D structures views,
during the construction phase, and after completion, in order to aid model
construction.
The main features of the SIG program are:
·
Structure input is in the form of typical
cross-sections of the complex body. Normally, the cross-sections are chosen at
points where the structure features change - such as at the start or end of
wings, etc. The user need only define as many cross-sections as will accurately
describe the structure when linear interpolation is used. Typically a structure
such as a jet fighter requires between 10 and 20 user defined cross-sections
for the generation of its structure.
·
A wire grid geometry is generated by SIG
for the complete structure, and does not require separate modelling for
different parts. A unique system of dividing complex cross-sections into tagged
curves enable the program to achieve a validly joined gridded geometry for
examples such as an aircraft where both wings and a canopy are linked to the
main fuselage.
·
Model generation with the same input file
at various frequencies is possible.
·
Segment length can be varied throughout
the structure. This reduces computational time when longer segments are used in
structure regions far removed from antennas. (This feature has not fully been
implemented in the current version of SIG GUI, and requires the user edit a
text file to achieve this at this time).
·
Cutting planes and angles can be specified
to remove parts of the structure at the user's discretion in order to reduce
problem size. (This feature has not fully been implemented in the current
version of SIG GUI, and requires the user edit a text file to achieve this at
this time).
·
Segment radii are automatically calculated
by the package such that the total wire surface area is approximately twice the
surface area of the actual structure. Each segment is assumed to be associated
with a square grid, and the radius is calculated as: 
. A radius adjustment factor, 
, may be specified in which case the radius will be
calculated as: 
.
·
The spacing between interpolated
cross-sections is calculated to ensure that the average length of the linking
segments is equal to the user specified target segment length. Even when
structure dimensions are changing between user-defined cross-sections,
approximately correct longitudinal segment lengths are generated.
·
Symmetry about the x- and y-planes can be
specified. In such cases, the segmentation takes this fact into account, and
segments abutting the symmetry planes will be half the normal length; no
longitudinal segments will be produced on the symmetry plane. (This feature has
not fully been implemented in the current version of SIG GUI, and requires the
user edit a text file to achieve this at this time).
·
Effective visualization is provided via the
graphical interface and SuperNEC.
·
The SIG program is also suitable for
discretizing simple problems such monopoles on rectangular ground planes (3
user cross-sections required), fan dipoles (4 user defined cross-sections
consisting of a single point per curve can be used), conical wire antennas and
the like.
The following
section labels all the buttons and controls in the SIG Interface which are
referenced to in proceeding sections.
A-Drawing Axes
B-Main Controls
(see section below)
C-Current
cross-section z-value display box (units: Metres)
D-Current
cross-section number edit box
E-New
cross-section button
F-Delete current
cross-section button
G-Cross-section
slider
H-Current x and y
coordinates (contains values when drawing) (units: Metres).
a-Line draw button
b-Interpolated
curve draw button
c-Line(s) select
button
d-Copy button
e-Delete button
f-Load curve from
workspace button
g-Zoom in button
h-Curve tag Number
box
i-Semi-circle draw
button
j-Point draw
button
k-Line flip button
l-Paste button
m-Snap to grid
button
n-Scale line
button
o-Zoom out button
SIG GUI projects
are saved in a .spf (SIG Project File) format. A SIG GUI project file can be
opened by selecting FILE->Open and selecting the desired project file in the
file browser window.
To save a project,
select FILE->SAVE, or the FILE-> SAVE AS menu option, and choose a filename
and location to store the project file. It is recommended that work done in the
SIGGUI is saved as a project (/.spf) file rather than a .grd (.grd files should
only be used for exporting purposes) as there is enhanced editing functions
(.grd files will be handled in later sections).
The SIG GUI makes
it easy to define the cross-sections of your complex structures by having a
number of predefined built in lines types such as single points, straight
lines, interpolated lines and semi-circles. Lines of these types are added by
simply selecting the appropriate line type button and clicking on the desired
locations of the points to from the curves, in the SIG GUI axes (above label A). To end the drawing of a line either
double-click when placing the last point or press one of the Main Control
buttons. The drawing of a semi-circle line is automatically ended when the
locations of the two end points have been selected.
Each time a new
line is drawn the tag number defined by the Tag number box (above label h) is assigned to the line. This can
later be modified if necessary.
Single points are
added by selecting the Point draw button (above label
j) and clicking the desired point locations.
Straight lines are
added by selecting the Line draw button (above label
a) and selecting desired points making up the line structure.
Smooth or
interpolated lines are added by selecting the Interpolated curve draw button (above label b) and clicking the major points through
which the interpolation will run. The default number of points making up the
curve is 50. This can later be changed to achieve the desired level of
smoothness for the curve.
Semi-circles are
added by selecting the Semi-circle draw button (above
label i), and selecting the two end points of the semi-circle. The
semi-circle will be drawn anti-clockwise from the first end point to the second
end point. These curves can be later be edited to form an oval and/or arc.
Lines can be added
from information stored in a workspace variable by using the workspace button
(above label f). The line added will be of the Straight Line type. The
workspace variable may have one of the following formats:
When the
snap-to-grid toggle button is depressed, any subsequent drawing functions will
add points on grid intersections. If the snap-to-grid option is selected,
moving of curves and editing of major points for interpolated lines or straight
lines will take place in grid spacing increments.
Before a line(s)
may be selected the SIG GUI window must be in Edit mode by making sure the Line
Select button (above label c) has been depressed.
Once in edit mode
a line can be selected by either Right or Left clicking on the line. Multiple
line selections can be made by either holding down CTRL and Left-clicking the
lines or by simply Right-clicking the additional lines.
Once a line is
selected, the colour of the line changes to magenta. The line will revert back
to it’s original colour as soon as it becomes unselected again.
To unselect all
lines, right-click an area of the axes not containing any curves, or to
unselect a single line, hold down CTRL and left-click the line to be
unselected.
Note: Only lines
in the current cross-section may be selected.
The SIG GUI offer
the ability to undo modifications made to your project and redo any undo
commands performed by mistake. The undo and redo commands are invoked by using
the menu items EDIT->UNDO and EDIT->REDO respectively.
When starting a
new project, the first cross-section is automatically created and given the
default value of z = 0m. The following sections will detail how new
cross-sections can be added, deleted and how the user can switch between
cross-sections, and change their associated z-value.
New cross-sections
can be added by making use of the new cross-section button (above label E) and entering in the required z-value
for the new cross-section. The new cross-section will be added after the
current cross-section and therefore the z-value entered in must be larger than
the current cross-section’s z-value and smaller than proceeding cross-sections
z-value (in the case of inserting a new cross-section between two existing
cross-sections).
The only exception
to the above rule is when requiring to add a new cross-section before the first
cross-section. In this case the z-value entered in must be smaller than that of
the first cross-section’s z-value.
To delete the
current cross-section, simply press the delete cross-section button (above Label F).
To modify the
current cross-section’s z-value, from the SIG GUI menu select
EDIT->Cross-section z-value.
The user may
change between cross-sections by making use of the cross-section slider (above label G), or by entering in the desired
cross-section number in the cross-section number box (above
label D).
As mentioned above
each curve in a cross-section contains a tag number identifier. When drawing
lines, this tag number can either be automatically assigned (without any
intervention), or can be manually assigned by selecting the required tag number
in the Curve Tag Number box (above label h). This
selection must take place after the required line type button has been
selected, but must performed before
starting to draw the line.
Once lines have
been drawn, the tag number(s) can be edited by firstly, selecting the line(s),
and then making use of the SIG GUI menu EDIT-> Curve(s) Tag No. menu option.
In order to copy a
line(s), make sure the line(s) are selected and then press the Copy button (above label d). Lines can then be pasted by using
the Paste button (above label l). When lines are
pasted to the same cross-section as they were copied from, new tag numbers are assigned to the copied
curve(s) and the location is marginally offset from it’s original copy location
in order to aid user editing. When a line(s) is pasted to a different
cross-section as it was copied from, the original tag number(s) and location
will be retained for the new curves. A line may also be pasted of type
‘Straight lines’ by using EDIT-> Paste as type ‘lines’. This feature may be useful
in the case the user wishes to create a complex line containing sharp points,
of which as a first iteration, can be created out of a semi-circle or
interpolated line curve.
This section will
discuss the various editing functions that can be performed on the various line
types. The edit functions are entered by making use of the axes context menu.
This menu becomes visible when right-clicking an unselected line (with no other
lines selected).
To change the
position of a line(s), select Move from
the context menu. The position of the line can then be altered by moving the
mouse. This editing function is exited by any mouse-click. To move multiple
selected lines, right click the drawing axes (after lines have been selected)
to bring up the context menu, and follow the procedure for a single selected
line.
If the snap-to-grid
option is on, the selected line(s) will only move in increments equal to that
of the grid spacing.
To edit the major
points making up a line, select the Edit
Points option from the context menu. This will then place green circles on
the critical points of the curve. These points can then be edited by
individually selecting them and moving them to the required position. The user
can also manually enter in the coordinates for a point by holding down SHIFT
and left-clicking a green circle. The
end points of a semi-circle can be edited to increase the arc-length and the
center major point can be edited to create an oval line. The user must make use
of scaling in order to change the major radius value of a semi-circle line.
A line can be
rotated about it’s first point by selecting the Rotate option from the context menu, and moving the mouse around
this point to the desired angle of rotation.
The number of
points making up an interpolated line or semi-circle line can be edited to
achieve the desired level of smoothness. Select No. Points from the context menu to enter this function.
A new point can be
added to a straight line and interpolated line by right-clicking the desired
position for the new point on the line, and selecting the Add Point option from the context menu.
The overall size
of a line can be increased/decreased by a user defined factor value. To perform
this function, select the Scale button (above label n).
The line(s) will then be resized, maintaining the position of the first point.
Scaling must be used if the user wished to change the major radius of an
already added semi-circle/oval line.
Selected line(s)
can be reflected about the x or y axis by selecting the Flip button (above label k).
The x and y coordinates
for a selected curve can be exported to a Matlab® variable, which can then be
editing using Matlab® functions etc. To invoke this function, select the EDIT->Send
Curve(s) to Wkspace Var -menu option.
The Matlab® variable will contain the n coordinates
with an ‘x’ field containing n x 1 x-values and a ‘y’ field containing n x 1
y-values.
To zoom in on the
current axes, select the Zoom-in button (above label
g) and drag the zoom-in rectangle over the desired area. To zoom out,
select the Zoom-out button (above label o). This
will return the axes to the set Axis limits value.
The following
section will describe the various grid functions\ modifications that can be
performed to aid model creation.
To display/hide
the x-grid, select the VIEW->X
GRID->DISPLAY option. Similarly follow the same procedure for showing/hiding
the y-grid.
The spacing of the
grid, used as a visual aid and for functions such as snap-to-grid, can be
altered by selecting the VIEW->X GRID->GRID SPACING option for the x-grid
and VIEW->Y GRID->GRID SPACING option for the y-grid.
The grid labels
options found under VIEW->x Grid->Labels->manual and VIEW->y
Grid->Labels->manual, allows the user to manually specify the axes numbering
for each axis. The user can also set the grid labelling to Auto, in which case
the SIG GUI will determine the best labelling for viewing and editing purposes.
The axis limits
can be changed by selecting VIEW->Axis Limits and entering in a matrix of
the form [x-min value, x-max value, y-min value, y-max value].
The axes aspect
ratio may be changed by selecting VIEW->Keep Aspect ratio. When “Keep Aspect
ratio” is set to on, 1 unit of increment in the x direction is equal to the
same unit of increment in the y direction and thus ensuring that images to not
appear distorted. When set to off, the axes are stretched to fill the window.
The curves to be
displayed in the current cross-section can be defined by using the VIEW->Curves->Manual
menu option, and entering in a matrix of the tag numbers of the required curves.
The user may also wish to display curves from other cross-sections in order to
aid model design by using the VIEW->Cross-sections->Manual menu option.
The curves from other than the current cross-section will be displayed as
dotted lines, and can not be selected in the current cross-section. The curves that
will be displayed in this case is also limited to those set by the View->
Curves menu option.
A .grd file
created by the SIG GUI or from the original SIG program can be opened by using
the FILE->Open menu option and selecting the .grd file extension in the file
browser. All the curves read from the .grd file will be of the ‘straight lines’
type. Currently, the SIG GUI does not support CP, GM and SY commands, these
commands will be ignored
A .grd file can be
generated by using the Generate -> Grd file menu option, and entering in the
segmentation frequency to be used. These files and .grd files written in the stand
alone version of SIG can be opened in SuperNEC by using the snsigfile structure
assembly or by selecting the “Readfile” option in the stand alone version of SIG.
The SIG GUI window
can be used to generate SuperNEC m-file assembly code, which the user can later
edit to for example add variables, add curves manually, make structural changes
etc. The procedure for creating an m-file assembly from the SIG GUI is as
follows:
In order to view
the gridded representation of the current cross-sections from the SIG GUI,
select the menu option GENERATE->3D Structure View. This will then prompt
the user for the segmentation frequency (frequency at which segments are set to
roughly 0.1*wavelengths).
Please note the 3D
structure view may take a couple of minutes to load, depending on the size and
frequency of the structure to be processed.
The tutorials presented
in this section will help the user familiarize themselves with the operation of
SIG and the SIG GUI interface. The first example will examine an generic
“aircraft” structure, while the second example will look at a patch antenna
with cut-out slot example.
This tutorial is
aimed at familiarising the user with the SIG GUI, and demonstrating the use of
the SIG GUI for a complex structure containing various extrusions. The generic
“airplane”
Figure 1: Aircraft structure
Figure 1 shows the plan view, side view and front view of a
generic "airplane" structure. The cross-sections that will be used to
construct the structure is also shown.
Note: A cross-section is used where ever structure characteristics
change in a discontinuous manner.
Figure 1 also shows the six cross-sections with the tagged curves.
The user should check that the curve definitions do not violate any of the
rules for curves. The main ones are:
·
Two curves in one specific cross-section
are considered joined when a point in both coincide; the coincident point must
be entered for both joined curves.
·
Only the end of one curve may join the
midpoint of another; i.e. no two curve midpoints may be joined. Any number of
curve end points can join together. Any number of curve end points may also
join one curve mid point. Both ends of a specific curve can join another
curve(s).
·
Curves may not join themselves; cases of
closed curves must be artificially divided in two to avoid this from happening.
·
Curves which occur in two cross-sections
must have the same tag number; this will ensure a “wing” curve which exists on
one curve will be extrapolated to the same "wing" curve on the next
cross-section. If tag numbers differ, this "wing" will terminate in
the current cross-section and restart in the next. If a curve only exists in
one cross-section then it will be represented as a simple wire protruding from
the structure.
This section describes the cross sections defining the structure.
Please refer to figure 1 above.
This tutorial will
investigate the creation of a patch antenna structure containing a shorting
wall, v-slot cut-out, and small ground
plane. This example is by no means a real antenna, but rather is used to
illustrate the capabilities for plate structures. The structure we wish to
create is shown in figure 4 and 5 below:
Figure 4: Patch structure with slot and shorting wall
Figure 5: Dimensions of patch structure
In order to create this structure, we will require 5 cross-sections to
define this structure. These are shown below, along with the corresponding tag
numbers used for each curve. It is recommended that the x and y gird spacing in
the SIGGUI is set to
0.25m and that the snap to grid option is selected. This will facilitate easy
model creation and editing.
Figure 6: First cross-section at z=0m
The first cross-section
is created at z=0m. The ground plane is constructed from two curves (Tag no. 1
& 2) to accommodate the junction of the shorting wall. The surface consists of 3 curves (Tag no.s 6,5 & 4).
Curve tag no. 5 is 0.25m in length and used to later accommodate the slot.
Figure 7: Second cross-section at z=0.1
The second
cross-section is identical to the first and exists at z=0.1m.Note this is the
last time that curve tag no 5 will appear in any of the cross-sections. That is
the gridding from the first definition of curve tag no 5 will end, and hence
create the start of the slot.
Figure 8: Third cross-section at z=0.4
The third
cross-section is taken at the centre of the patch and exists at z=0.4m. If you
have used snap to grid and set your grid spacing to 0.25 as suggested above,
then you can either turn off snap-to-grid to create the correct length curves
4,6, or set your grid spacing to 0.125, or you could simply create these two
curves having the same dimensions above, and then edit the curves points
manually by holding down shift and right clicking the appropriate point on the
green circle.
Figure 9: fourth cross-section at z=0.7
The fourth
cross-section occurs at z=0.7m. Notice the introduction of a new tag 7, this is
to ensure the gridding where the slot previously was. The only difference
between this and the second cross-section is the new tag number.
Figure 10: Fifth cross-section at z=0.8
The final
cross-second is identical to the previous cross section, as expected. The final
structure modelled in SuperNEC at 300Mhz is shown below:
Figure 11: Model in SuperNEC segmented at
300Mhz