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After reading the work, and before you begin to write, try to fit the analysis into proper context. Keep in mind the setting in which a decision maker-the analysis’s and its critique’s consumer-will view the work.
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,\, SIMULATIO~J Or’ R/IPID SHIP um,0l1Drnr, BY HF.LICOPTF:R
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Bruce F. :Powers
Center for !lava] Analyses
University of r o =hester*
Arlington, Virginia
Martin Goldberq
Industrial Engineering Department
Illinois Institute of Tc chnoloqy
Chicago, Illinois
Introduction and Summary
A ship with helico:)ters aboard arrives
in the vicinity of a shore line. ‘l’he com.’llander
intends to ooerate the helicooters so as to
unload the ship as raoidly as· possible. The
ship’s c a rgo is to be delivered to a soecific
point ashore by the helico~ters. The arrival
rate of the cargo at that point will neasure
the effectiveness of the \L’1loading ooeration.
The co:-:-…~ander must decide at what distance
to station the ship from the unloadinq ooint
ashore, how rnany of his helicopters to use
for the unloading, and the grouoinq of the
participa ting helicopters. He knows, or
has reliable estimates of, the ti~ e scent by
helicopters while loadinq or refueling on the
ship, unloadinq at the ooint ashore, and
flying b e tween . the ship. and ooint as h ore.
This paper describes a simulation model
“”hich can assist the comr.iander with his
decisions.
Discussion
This problem is faced by the amphibious
forces of the U.S. Navy and exercises are
conducted by the Na\~ to train forces and
to test different policies f or helicopter
unloadin g s. The develop::’.ent of a model of
the unloading proce ss would permit testing
alternate unloading policies without the
expense of sending a shio to sea. It wo~ld
permit examination of the imolicat ions of
changes in the design of the ship, the design
of helicopters, or the capacity of the
unloading point.
Anothe~ problem is also faced by the
Navy. If victims of a disaster such as a
flood or earthquake require evacuation, the
Navy would pr o bably as si gn a shio with
helicopters to the task. For medical reasons
or because of the threat of loss of life, the
helico?ter e v acuation may have to be conducted
as rapidly as possible. The aoolicability.of
a model of ship unloading could readily be
transferred to the evacuation problem.
The m~de l could also be useful for
examination of harbor ooeration oolicies
where sufficient berthing space for waiting
ships is unavailable. Under such conditions,
the use of helicopters for unloadinq shies
while in the roadstead might be an attractive
alternative to having the ships wait for
berthing space. The model can aid dcvelooment
of costing information to permit choice among
these alternative harbor management policies.
De scriotion of the System
The shio arrives in the unloadinq area
and takes stati o n as shown in Figure 1.
D
HELICOl’TEAS
Up,;lOAOll SHORE Llf\: E
Figure 1. Sketch of Sy5tem
Helicopters are stored on the ship with • Research done while on sabbatical leave at IIT.
400
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rotors folde d to conserve soace. When needed
to ferry cargo, helicooters are brought uo to
the fli g ht de ck and o ren a red for flig h t.
Because helicooter storace canacitv beneath
the flight deck exceeds the flight. deck
caoacity when r o tors are unfolded, se veral
deckloads of helicooters are often available
for unloading the shio. Helicont e r s c oe ra-
tinq fr o m the ship are gro uoe d into waves.
In gene ral, a d e ckload of helicooters makes
up more than one wave and ~ore th a n o~e deck-
load is used for an unload ing. The wav es
flow through a syste m consisting of two
primary no6es, the s hi o a n d t h e unloading
point (called the lan din g zone). The activity
of the first wave, which i s tyoical, consists
of an initial launch without cara o , move~ ent
to a marshaling are a near the shi p , return
to the flight d e c k when a ll waves are airborne,
loading of carqo, launch for the transit to
the landing zone as hore, landing in the zone,
unloading of car g o, launch for return to the
ship, and re-landina on the shio fo r loading
of more cargo and/or ref\!eling. The cycle
is then reoeated bv the first and other waves
until the ship’s cargo is unloaded.