Simulation of a Frigate Warship Model on a PC
WIPL-D Pro is a frequency-domain Method ofMoments (MoM) based code which enables very
accurate EM simulation of arbitrary 3D structures.
Owing to application of sophisticated techniques, verylarge structures are simulated on PC computers orinexpensive workstations.

MoM Efficiency
WIPL-D software applies very sophisticated higher
order basis functions (HOBFs) on a quadrilateralmeshing. 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 arecapable 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 ofHOBFs is entirely automatic, although the user canincrease the accuracy of approximation.

Model Description
Frigate warship model is 117 meters long, and 12.6
meters wide. The ship is placed above a PEC planethat models the influence of the sea. A monopole
antenna is placed on top of a 24 meters highcommunications tower. The simulation frequency is
240 MHz, which makes the frigate about 94
wavelengths long.

Direct Solution & Out-of-core Solver
Direct solution based on LU decomposition is thedefault solution technique used in WIPL-D Pro. When
there is not enough RAM for the incore solution, outof-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 insimulation time, usually up to 20% of the incore
solution time.

Smart Reduction of Expansion Order
This feature is especially suitable for antenna
placement problems. It is based on adaptive reductionof current expansion order over parts of the model
which are distant from the antenna or in shadow. Thisway, 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 theuser to be in shadow are additionally treated.
Expansion orders on all patches in shadow aredecreased uniformly, in addition to the distance-to-theantenna factor.

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 theout-of-core solver, the hard drive can be used asstorage 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.

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contactus@wipl-d.com

In case of the antenna location on the top of thecommunication tower, the number of unknowns can be
reduced significantly while maintaining an acceptableaccuracy of radiation pattern results. As the number of
unknowns decreases, so does the simulation time, asshown in the table below.
Number of unknowns

Simulation time [hours]

78300

8.28

62462

4.49

51131

2.76

40017

1.5233584

0.97

The number of unknowns was decreased about 2.3
times while the simulation time was decreased about
8 times without significant discrepancies of thecalculated radiation pattern.
The radiation pattern in the transverse plane,
perpendicular to the ship bow-stern axis is shown in
the figure below 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 somediscrepancies occur for θ>65°. However, calculations
are still stable and give a very good estimation of theelectromagnetic 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.

www.wipl-d.com
contactus@wipl-d.com