ASSIGNMENT SHOULD BE ATTACHED. THIS IS NOT A SUMMARY… Your critiques are limited to 300 words. Good critiques are lean, crisp and, above all, illuminating. Good critiques also stand on their own-not requiring the reader to be intimately familiar with the analysis.
The following will help you get started:
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.
Next, identify the key assumptions that underlie The work Identify them explicitly (sometimes the author will help you), and decide the degree to which you agree or disagree to which you agree or disagree substantially with any particular assumptions, note why.
Identify alternative assumptions, if appropriate and possible. Pose at least one competitor assumption (usually, one you’d prefer), and contrast its viability.
If the work is not current, make an issue of it only if new information has become available that refutes the work. (It is generally most appropriate to view the work from the time perspective when it was done.)
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Finally, decide whether or the author’s conclusions flow from the works logic and evidence. If not jot down why not.
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,\, SIMULATIO~J Or’ R/IPID SHIP um,0l1Drnr, BY HF.LICOPTF:R I ‘
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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.
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HELICOl’TEAS
Up,;lOAOll<G POINT
SHORE Llf\: E
Figure 1. Sketch of Sy5tem
Helicopters are stored on the ship with 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.
• Research done while on sabbatical leave at IIT.
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