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WIPL-D Pro is a frequency-domain
Method of Moments (MoM) based code which enables very accurate
EM simulation of arbitrary 3D structures. Owing to application
of sophisticated techniques, very large structures are simulated
on PC computers or inexpensive workstations.
MoM Efficiency
WIPL-D software applies very sophisticated higher order basis
functions (HOBFs) on a quadrilateral meshing. This means that
basis functions are higher order polynomials instead of simple
linear (rooftop) functions. Hence, in case of equal number of
HOBFs and rooftops defined over a surface, HOBFs are capable of
expressing more dynamic current distribution. Owing to this
efficiency, significantly larger structures are quickly
simulated on cheap PCs than by using other methods/solvers.
Application of HOBFs is entirely automatic, although the user
can increase the accuracy of approximation.
Direct Solution & Out-of-core Solver
Direct solution based on LU decomposition is the default
solution technique used in WIPL-D Pro. When there is not enough
RAM for the in-core solution, out-of-core solution can be used
instead. The out-of-core solver employs the PC hard drive for
matrix storage during calculations. This causes a small increase
in simulation time, usually up to 20% of the in-core solution
time.
Smart Reduction of Expansion Order
This feature is especially suitable for antenna placement
problems. It is based on adaptive reduction of current expansion
order over parts of the model which are distant from the antenna
or in shadow. This way, the number of unknowns is reduced 2-10
times depending on the model, while very good accuracy of
calculated radiation pattern or coupling between multiple
antennas is preserved.
In addition, regions of the platform regarded by the user to be
in shadow are additionally treated. Expansion orders on all
patches in shadow are decreased uniformly, in addition to the
distance-to-the-antenna factor.
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Figure 1. Frigate warship
model |
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Table 1. Numbers of
unknowns and simulation times
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Number of unknowns |
Simulation time [hours] |
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78300 |
8.28 |
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62462 |
4.49 |
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51131 |
2.76 |
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40017 |
1.52 |
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33584 |
0.97 |
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Model Description
Frigate warship model is 117 meters long, and 12.6 meters wide. The ship
is placed above a PEC plane that models the influence of the sea. A
monopole antenna is placed on top of a 24 meters high communications
tower. The simulation frequency is 240 MHz, which makes the frigate
about 94 wavelengths long.
The full model, without any symmetry
planes, requires 78300 unknowns, which is equivalent to 49 GB of memory.
This requirement is not easily met by any workstation on the market.
However, so much RAM is not needed for this simulation. Applying the out
of core solver, the hard drive can be used as storage during
computations, which makes almost any PC a powerful simulation
environment. The frigate model was simulated on a USD3000 PC containing:
• Intel Core 2 Quad CPU at 2.83 GHz clock,
• 8 GB of RAM DDR2,
• 300 GB hard disk.
The complete simulation without order
reduction, using the out-of-core solver and a multithreaded WIPL-D Pro
3D EM solver, takes 8.28 hours. Time savings due to smart reduction of
expansion order depend on the antenna position on the warship. In case
of the antenna location on the top of the communication tower, the
number of unknowns can be reduced significantly while maintaining an
acceptable accuracy of radiation pattern results. As the number of
unknowns decreases, so does the simulation time, as shown in Tab. 1. The
number of unknowns was decreased about 2.3 times while the simulation
time was decreased about 8 times without significant discrepancies of
the calculated radiation pattern.
The radiation pattern in the transverse plane, perpendicular to the ship
bow-stern axis is shown in Fig. 2 for different degrees of smart order
reduction. Angle θ is measured from the xOy plane up, so θ=90°
corresponds to the monopole antenna axis (towards the sky). The shape of
the radiation pattern doesn’t change as the number of unknowns is
decreased, while some discrepancies occur for θ>65°. However,
calculations are still stable and give a very good estimation of the
electromagnetic behavior of such a large structure. In case of the
maximum order reduction, a 94 wavelength long frigate is modeled by
33584 unknowns and simulated in around 1 hour.
Figure 2. Gain in the transverse plane
for different degrees of smart order reduction
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