
OVERVIEW
VisualSMP
is a suite of tools used in the prediction and analysis of a ship's seakeeping
and loads characteristics. Included in VisualSMP is the US Navy's strip theory
based ship motion program (SMP), US Navy's seakeeping analysis program (SEP),
US Navy's standard time history program (STH and ACTH), and US Navy's
seakeeping program for SWATH (SWMP). VisualSMP has a graphical pre and
postprocessor, together with tools to extend and refine the functionalities of
SMP. VisualSMP is an easytouse and reliable tool for predicting ship motions
and loads for monohull, SWATHs and regular catamarans and graphically
evaluating the calculated motions. VisualSMP is also a unique tool for
evaluating ship motion reduction measures such as bilge keels, rudders, fixed
fins, controllable fins/rudders, moving weights and various antiroll tanks.
HISTORY OF VisualSMP
US
Navy's SMP was the very first strip theory ship motion program.
It is a product of more than 30 years of US Navy's research,
from late 1960s to late 1990s. In 1999, US Navy selected Proteus Engineering,
which was later acquired by Alion Science and Technology, to make it more user
friendly and available to commercial customers. In addition to creating a
graphical pre and postprocessor interface, Alion Science and Technology has
added many new features to VisualSMP to extend and refine the functionalities
beyond the original SMP.
Alion
Science and Technology is constantly updating and improving VisualSMP to
reflect the most recent ship motion research and developments in US Navy,
Alion and the industry as a whole. We are committed to keep our program to
be the best of its kind and to provide the best technical support to our
customers.
MOTIONS PREDICTION and LOAD CALCULATION
VisualSMP
calculates 6DOF rigid body motions, absolute motions of any specified
points and the relative motions of specified points relative to waves in
both regular and irregular waves. The irregular seas are modeled using
either the two parameter Bretschneider, the three parameter Jonswap, or
the six parameter OchiHubble wave spectral models. Both longcrested and
shortcrested results are provided; shortcrested waves are generated
using a cosine squared spreading function. Motion outputs include
displacements, velocities and accelerations. Load outputs include vertical
and transverse shear forces, longitudinal and horizontal moments, and
torsion moments at user's specified locations. Output for regular waves is
in the form of RAO and/or transfer functions. Outputs for irregular waves
are response spectra and various statistics that may be used in ship
design and performance assessment. VisualSMP will calculate the
probabilities and frequencies of submergence, emergence, and/or slamming
occurrence, slamming pressure/force, MSI (motion sickness incidence) and
MII (motion induced interruptions, i.e., tipping and sliding) for various
locations on the ship. It also estimates added resistance in waves. Based on the user specified motion
limits and criteria, VisualSMP will calculate the Operation Index (OI) for
all the speeds/headings or a subset of speed/heading combinations.
VisualSMP outputs tremendous amount of data in text files. To present
these data logically and graphically, VisualSMP has convenient plotting
tools to produce high quality 2D and polar plots.
Alion
has
developed the graphical pre and postprocessor using the Microsoft
Windows GUI. These tools speed the data input process and provide
graphical tools to view the computed results. VisualSMP input models
consist of hull offsets, appendage dimensions, and controller
coefficients. The hull offsets are described to the system as points on
sections, including the stem and stern profile. Both transverse and
longitudinal knuckles are allowed. New
Versions
of VisualSMP feature powerful geometry input and manipulation utilities.
These utilities make preparing offsets almost an automatic process. The
user may import the offset table from FASTSHIP in an IDF format, or
prepare the offsets in a GHS GF style text file. The offset points may go
above the waterline. After IDF or GF file is imported into VisualSMP, the
user can use 'Modify Sections' to clip the sections to a particular
waterline, and then use other utilities to make point distribution to the
user desired level section by section.The
user may input up to 70 stations and 70 points per station, and may choose
from the following list of appendage types to include in the calculations:
Sonar Dome, Bilge Keels, Passive Fins, Active Fins, Shaft Brackets,
Propellers, Propeller Shafting, Skeg, Rudders, and Roll Tanks.
In addition to the many text output files, VisualSMP presents
its output in plots in the forms of RAO plots and speed polar diagrams. The
polars show the ship's response for any motion/load as a function of speed and
heading, and can also show the effect of an imposed limit on the ships
operation. When the ship's motion/load has exceeded a userdefined limit on one
of the motions, the contours for those speeds and headings are drawn in red to
highlight the limit of operation. These response contours can also be presented
vividly in a continuously colorcoded (or colorfilled) polar plot. The user
can also specify a set of operations limits on various motion/load responses
and VisualSMP will calculate the operational index based on these limits.
Polar plots are recently extended to various statistics values of every ship
motion and load responses: the Bandwidth, the Most Probable Maximum Response,
the ZeroCrossing Response Period, the Average Response Period, the Probability
of Exceeding A Specified Value, the Number of Occurrence of Exceeding A
Specified Value.
RECENT
DEVEOPMENTS In VisualSMP
Among
many other things and past improvements, the most recent Alion additions and
improvements are: (1) A suite of utilities to easily modify, refine and prepare
the hull geometry; (2) Fully functional OchiHubble family of wave spectra; (3)
Motion and relative motion time histories outputs for shortcrested waves; (4)
Calculating
the cargo latching forces at the specified deck surface and point in both
longcrested and shortcrested waves; (5)
Quasinonlinear roll restoring force, i.e., using the actual GZ curve in
transverse motion and loads calculations; (6) Calculate and output of the
response band widths; (7) Calculate and output of the ZeroCrossing
Response Period and the Average Response Period; (8) Calculate response
statistics, such as the Most Probable Maximum Response in a specified
length of time, based on the response's actual bandwidth instead of using
narrowband assumption; (9) Calculate the probability of exceeding a
certain response (motion or loads) level in a specified length of time
based on the response's actual bandwidth; (10) Calculate the number of
occurrences of exceeding a certain response (motion or loads) level in a
specified length of time based on the response's actual bandwidth; (11)
Calculate the probability of exceeding and number of occurrences of
exceeding a certain response level for a mission profile, which will
include all the speeds and headings for various different combinations of
wave heights and wave periods.
SEAKEEPING ANALYSIS
The
Seakeeping Evaluation Module (SEP) can be used to estimate the
seaworthiness of SWATH and monohull ships early in the design process.
Estimation of the seaworthiness of ships can be useful in several ways. In
early design studies, prediction of the effect of hull form modifications
on ship motions can have an impact on the design, permitting the selection
of a seaworthy hull form, from among those which meet other design
requirements. The ability to readily analyze the relationship between hull
form modifications and seaworthiness can allow consideration of many hull
forms in a short period of time. Once a ship has been built, estimation of
seaworthiness utilizing frequency domain prediction methods can facilitate
prediction of the potential ability of the ship to carry out a new
mission. This facilitates consideration of the effect of hull form
modifications on performance.
There are three major components used in the
seakeeping evaluation; the rigid body motion transfer functions for the
particular hull form, the data describing the probability of occurrence of
various sea conditions, and the seakeeping criteria which describe the
degradation of performance due to ship motions. The transfer functions must be
generated using VisualSMP regular wave modulefor
monohull ships or SWATH module for SWATH ships.
Required input data for the SEP includes motion transfer functions which have
been generated by either the SWATH module or SMP regular wave module as well as
data files which contain results from analysis of Spectral Ocean Wave Model
(SOWM) data. This data defines the joint probability of occurrence of
significant wave height, spectral modal (peak) period, and wind speed for
various geographical locations.
Although
there are limitations to the analysis used in SEP, it provides the means
of easily, quickly, and consistently estimating the seaworthiness of hull
forms for a range of missions, giving consideration to a wide range of
spectra and their probabilities of occurrence at a large number of
geographical points. This method of predicting seaworthiness is useful in
comparing the performance of a variety of hull forms.
TIME HISTORY
GENERATION
VisualSMP
's STH module uses transfer functions to generate time histories for the
waves and the vessel 6DOF motions in irregular seas as well as the time
histories of motion and relative motion of any points. Both the numerical
time histories and the cosine coefficients for use in visualizations and
simulations are computed. VisualSMP 's STH module not only generate time
histories for longcrested waves but also for shortcrested waves. If the
user specifies the normal of a deck, the STH module will calculate
the cargo latching forces at the specified deck point in both longcrested
and shortcrested waves.
SHIP MOTION VISUALIZATION
The VisualSMP visualization program uses the cosine coefficients and a geometry
model from an IDF mesh file (for example from FastShipT)
to simulate the ship in a seaway at a fixed heading and speed. The simulation
may be run at realtime, or at a processordependent speed. The model may be
rotated and viewed from any angle, and reference points (buoys) may be defined
to help visualize speed. The user's view may be either global (off the ship) or
from the bridge.
