WaveCalculator 1

machinebrainySoftware and s/w Development

Jun 8, 2012 (5 years and 3 months ago)

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NATIONAL WEATHER SER
VICE FORECAST OFFICE
, SEATTLE WA


June

2
8
, 2011


Jay A. Albrecht

Lead

Forecaster


WaveCalculator 1.
2


A Simple Java
-
Based Computer Tool for
Determining Wave Height and Decay





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WaveCalculator 1.2

A Simple Java
-
Based Computer Tool for Determining Wave Height and Decay

Overview:

Marine forecasters now use sophisticated wave models, such as

NOAA’s

Wavewatch III

and Environment Canada’s
Ocean Wave Model
, to determine sea heights and dominate wave periods for their area of responsibility.
Most w
ave
models

automatically account for surface wind speed, atmospheric stability, moving fetches,
interaction of different

wave groups
, and
the effects of complex
bathymetry to produce their results.

Wave models also have the capability
to pro
duce

results for different
wind
-
sea and swell
trains in the

wave spectrum.

Atmospheric forcing for
NOAA’s
Wavewatch III

model

is
provided by the GFS model
, a model that

typically
performs well in
forecasting the strength
,
movement
,

and timing of storm systems in the marine environment.

A
ll a
tmospheric models

will
occasionally
have difficulty

timing and placing

individual storm syst
ems
; w
hen
problems
occur
, the quality of forecasts provided by
the sophisticated wave models

will suffer

greatly

and forecasters

will
need
to revert to the use of old forecast tools
such as
nomograms (
or
Personal Computer (
PC
)
applications that mimic
thei
r result
s) to make their wave forecasts
.


Nomograms or PC applications also need to be used in lakes, bays,
estuaries, or bodies of water not within the domain of sophisticated global or regional wave models.

WaveCalculator 1.
2

is a simple Java
-
based

Graph
ic
al

User Interface

(GUI)

that allow
s

marine

forecasters

to
determine

significant wave height and dominate wave period
given wind speed

(
knots
)
, fetch

length

(
nautical miles
)
,
and
wind
duration

(
hours
)
. The

algorithm uses

a

series of

multidimensional
polynomial

regression formula
e

to
perform

computations

(described by
Freeman, 1985 and Bret
s
chneider, 1970
)
. The calculator
can also be used to
determine
swell decay

given an initial
swell
height
and period and a decay distance. S
pecifically, the calculat
or
determines the significant wave height

and period of
a

decayed swell at the end of
a

decay distance
,

and

it determines

the travel time from the initial location to the end of the decay distance.

Swell decay
formula
e,

as

devised by Monk
and Sverdrup, 19
47 and described by Titov, 1969
,

are

used in
WaveCalculator 1.
2
.

This calculator is an update to
WAVE.EXE (described in Albrecht, 1998), a

16
-
bit Visual Basic

3.0

application
that will not run on

modern

64
-
bit

operating systems or on non
-
Microsoft

comput
er

platforms
.

WaveCalculator 1.
2

will run on any operating system
where the Java run
-
time environment (version

jre
-
1.6 or greater) is installed.



Instal ling and Using WaveCalculator:

Download WaveCalculator.tar,
and then

extract it to an appropriate location on your computer. To run the
application, you will need to have the latest Java run time environment installed (jre
-
1.6 or higher). On a PC
running Microsoft Windows, you can use
freely available

compression softwar
e such as 7
-
Zip or WinZip to extract
the files. On a Linux box, open a command prompt,
change directory

to the location you placed the tar file, then
type:



tar

xvf


WaveCalculator.tar

Note that most

Linux distributions contain a variety of compression
and decompression utilities that can be used.

To install the application onto a NWS AWIPS system, it is recommended that the application be
placed

into
/awips/dev/localapps

so that the files will be
preserved in a system upgrade.



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veCalculator 1.2

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WaveCalculator.tar

conta
ins required Java libraries, WaveCalculator.jar (the Java executable) and an icon
(W
ave
.
png
).
In
Linux
, you

will need to

make the .jar file executable
by typing:
chmod a+x WaveCalculator.jar

in a
command prompt from within the installed directory.

Once in
stalled, you can create a desktop shortcut and assign W
ave
.
png

as the icon. Linux users will need to set up the
executable in
a

shortcut (like in a KDE Panel button

or one of various menus
) by typing the full path to the Java run
time environment and the p
rogram executable. For example, in AWIPS

if installed as described above,

this

might be:


/usr/local/jre
-
1.6.0_13/bin/java


jar


/awips/dev/localapps/WaveCalculator/WaveCalculator.jar


WaveCalulator 1.
2

GUI
. Answers provided are consistent with
wave and swell decay nomograms that were used
by marine forecasters prior to the widespread use of
PCs
.
Here, units are displayed in the default Imperial values.
Alternatively, users may select Metric units.

When you start the program, the GUI as shown in the figure above will be displayed.

If you want to use default
Imperial units, you can just start using the program. If you would like to use metric units, click Units
-
>Metric on the
menu bar. U
se the slider

bars on the left
-
hand pane to make significant wave height and dominate wave period
forecast
s

for given wind speed, fetch and duration entr
ies
. U
se the slider bars on the right
-
hand pane to make a swell
decay forecast given the height and period of the of
fshore swell and the distance offshore of the

wave or swell

observation.

Forecasts will
be immediately

displayed in the text boxes at the bottom of the

GUI

as the slider bars are
moved.





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Assumptions:

WaveCalculator 1.
2
, when run in the forecast mode, ass
umes that the wind is instantaneously started to the value
specified by the user, and that the wind blows at a constant rate over the specified duration and fetch (not very
realistic). Wave

heights and periods apply to the significant wave, a statistical v
alue defining the highest 1/3 of the
waves.

The significant wave height provided by this program in the forecast mode does not account for pre
-
existing swell or


wind waves;
nor

does

the algorithm
account for interactions between distinct wave and swe
ll groups.

Wave growth inherent to the algorithms used by this program do not account for changes in boundary layer


atmospheric stability. In reality, wave growth will be more effective

when air temperatures are much lower than sea


surface tempe
ratures and will be less effective when warm stable air is moving over a cold sea surface.

When determining swell decay, it is assumed that the initial values specified by the user refer to swell characteristics

o
utside

of

the wave generation area.


Sinc
e the swell decay algorithm uses
formulae

developed by Sverdrup and Monk, the initial fetch width of the swell
train that is being decayed is not considered. This will
result in

unrealistically high decayed swell height values for
tropical cyclones or sma
ll extratropical cyclones where the initial fetch width is small.

Wave forecasts and swell decay values provided by this program are consistent with those determined using

wave
forecast and swell decay

nomograms.

Methodology:


Fetch limited
significant
height

and dominate wave period

values are calculated using a third
-
order polynomial
equation that is a function of

the base 10 logarithm of
fetch and wind speed

using:





























































F
or
fetch limited
wave height and dominate wave period:










and









.

Duration limited significant wave height and dominate wave period values are calculated using the same third
order
equation
, but as
a function of

the base 10 logarithm of
duration and wind speed, where:










and











.
The significant wave height and dominate wave period will be the lessor of the
fetch
limited and duration limite
d values
.




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veCalculator 1.2

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As swell propagates well away from its fetch area, the dominate period of the swell train increases as given by the
following equation:





























is the period of the swell at the observation point at the start of
the decay distance,



is the period of the swell
at the end of the decay distance, x is the decay distance, g is gravitational acceleration, A is








, and r is
0.580.



Arrival time is a function of the change in period through the decay and is

given by the following:





















Height decay is calculated from:
























Where


= 2.5.



Height
Fetch Limited

Period
Fetch Limited

Height Duration Limited

Period Duration Limited




-
ㄮ㈰1㌰3㜷7㠶

〮㜲0〸0ㄱ1㈳2

㄰⸳1㠱8㤸9〴

㜮㘶7㤹9㘹6〷




0
⸰〷.㌵3㐵4㈲26

〮〰0〷0㤸9㐱4㈲

〮〸0ㄹ1㜹7㤹9

〮〴0㔰5㤳9㌷3




0
⸰㌵.㈱2㔳5㤵9

〮〰0㔲5〷0㈹2㐱

-
〮㈳0㌴3㈹2㠹8

-
〮ㄷ0ㄱ1㠱8㌹3




-
〮㜸0〷0㔴5㘹6

-
〮㐷0〶0㈸2㘵6

-
ㄮ㌳1㜰7㠳8㈲

-
〮㠰0ㄱ1㌳3㈸2




〮㠰0㌴3㤶9㜴7

〮㈹0㜳7㐶4㘳65

-
㌮〵3㠱8㤵9ㄳ

-
㈮〰2㜳7㠳8㘲




-
〮ㄳ0㔷5㔴5㜳7

-
〮〶0㈶2㜳7㘵6

〮〴0㈵2㠰8㔸54

〮〷0ㄱ1㤰9〲04




㈮㐴2㘲6㘳6㐳

ㄮ㔶1㌸3㔴59

㐮㘰4㔹5㠶8㠱

㈮㠵2㔱5〰0㔹




-
㈮㐴2㤳9㘲6㌹

-
〮㔰0㤴9㤰9㜵7

ㄴ⸴1㘳6〵0㜱

㤮㔸9㘹6㐴4㤴




-
ㄮ㈹1ㄸ1ㄳ1㔵

-
〮㤱0㠱8㠹8㐶4

-
㌮ㄴ3㌵3㔴5ㄶ

-
㈮〴2㘰6㌸3㔴




㈮㠳2㜱7㜹76

-
〮ㄵ0㜲7㠸8㠳8

-
㈱ⰳ2㔲5㜷7ㄲ

-
ㄴ⸶1㈱2㘹6㐴



Ta扬e
潦o
c潥晦楣楥湴n 景f Bret
s
chneider’s third order

best
-
fit

polynomial function.





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References:


Albrecht, J.

A., Forecasting the Development of Wind Waves and the Decay of Swell
.

Western Region Local
Software Application (LSA
-
17), 1998.

Bretschneider, C. L.
,

Forecasting Relations for Wave Generation. Look Lab/Hawaii, Vol. 1, No. 3. Honolulu:
Department of Ocean

Engineering, University of Hawaii.

1970.

Freeman, J.C., Marine Transportation and Weather
-
Sensitive Operations, Handbook of Applied Meteorology, David
D. Houghton editor, Chapter 35, 978
-
997.

1985.

Sverdrup,

H. U. and W. H. Munk, Wind, Sea

and Swell: Theory of Relations for Forecasting, U.S. Navy
Hydrographic Office, Pub. No. 601. 1947.

Titov, L. F., Wind
-
Driven Waves, Gidrometorologicheskoe Izdatel’stvo, Leningrad, 1969.

Program Code:


WaveCalculator 1.
2

was written in Java using
the
Netbe
ans 6.9.1

Interactive Development Environment (free
download from
www.netbeans.org

)
.
Contact the author (
jay.albrecht@noaa.gov
) for a copy of the source code.