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Military logistic problem
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christriddle@googlemail.c
science forum beginner


Joined: 10 Jul 2006
Posts: 12

PostPosted: Mon Jul 17, 2006 2:37 pm    Post subject: Re: Military logistic problem Reply with quote

Great, that's helped alot. Thanks very much!
Chris
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trooperwt@yahoo.com
science forum beginner


Joined: 14 Jul 2006
Posts: 1

PostPosted: Fri Jul 14, 2006 5:50 pm    Post subject: Re: Military logistic problem Reply with quote

Paul A. Rubin wrote:
Quote:
christriddle@googlemail.com wrote:
Thanks for replying.

To add more detail:

There exists x ports and a number of strat-lift and ships. The loads
for each are worked out before hand (i.e. a simulations could have 120
C130 loads, 20 C17 loads and 8 ship loads).
The loads are transported from one or more ports, and aircraft possibly
have to land and refuel on route depending on distances and loads.
Ships only have one load, and then they effectively disappear. Whereas
aircraft fly back and forth transporting loads.
At each port there are several variables, like gang/handler numbers,
loading bays/berths, aircraft handling equipment/ cranes, etc...
The start-lift/ships work day and night but with a limited number of
aircrew (that need resting ever so often). Loading/offloading times
depend of the size of the load and need a free (and rested) gang or AC
handler team to do this.


One question of the simulation would be: "What is the optimal number
of gangs/AC handlers and aircrew ratio (number of aircrews to aircraft)
to move everything in the fasted time possible?"

Thanks again.
Chris


Assuming that transit times, fuel consumption, loading/unloading times
etc. are deterministic (or you're willing to work with averages), this
sounds like it's amenable to a mixed-integer linear programming model.
The integer variables would be used to assign aircrews, set the order
for loading/unloading aircraft and/or ships (I'm assuming that ships and
planes need to queue up for unloading, rather than there being capacity
to unload simultaneously as many as might show up), enforce mandatory
rests and so on. If the scale of the problem is not too large, a MIP
model should work. The airline industry uses large MIP models for
scheduling aircrews, but their problems tend to be huge, and there are
people making a good living developing algorithms for those problems.

/Paul

I would recommend a discrete event simulation approach where you can
easily model the variation of the loads, mandatory rests, land and
refuel due to distance and load. You can run many scenarios and
identify consistent bottlenecks from run to run.

/Trooper
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Paul A. Rubin
science forum beginner


Joined: 02 Aug 2005
Posts: 5

PostPosted: Fri Jul 14, 2006 3:29 pm    Post subject: Re: Military logistic problem Reply with quote

christriddle@googlemail.com wrote:
Quote:
Thanks for replying.

To add more detail:

There exists x ports and a number of strat-lift and ships. The loads
for each are worked out before hand (i.e. a simulations could have 120
C130 loads, 20 C17 loads and 8 ship loads).
The loads are transported from one or more ports, and aircraft possibly
have to land and refuel on route depending on distances and loads.
Ships only have one load, and then they effectively disappear. Whereas
aircraft fly back and forth transporting loads.
At each port there are several variables, like gang/handler numbers,
loading bays/berths, aircraft handling equipment/ cranes, etc...
The start-lift/ships work day and night but with a limited number of
aircrew (that need resting ever so often). Loading/offloading times
depend of the size of the load and need a free (and rested) gang or AC
handler team to do this.


One question of the simulation would be: "What is the optimal number
of gangs/AC handlers and aircrew ratio (number of aircrews to aircraft)
to move everything in the fasted time possible?"

Thanks again.
Chris


Assuming that transit times, fuel consumption, loading/unloading times
etc. are deterministic (or you're willing to work with averages), this
sounds like it's amenable to a mixed-integer linear programming model.
The integer variables would be used to assign aircrews, set the order
for loading/unloading aircraft and/or ships (I'm assuming that ships and
planes need to queue up for unloading, rather than there being capacity
to unload simultaneously as many as might show up), enforce mandatory
rests and so on. If the scale of the problem is not too large, a MIP
model should work. The airline industry uses large MIP models for
scheduling aircrews, but their problems tend to be huge, and there are
people making a good living developing algorithms for those problems.

/Paul
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christriddle@googlemail.c
science forum beginner


Joined: 10 Jul 2006
Posts: 12

PostPosted: Fri Jul 14, 2006 12:00 pm    Post subject: Re: Military logistic problem Reply with quote

Thanks for replying.

To add more detail:

There exists x ports and a number of strat-lift and ships. The loads
for each are worked out before hand (i.e. a simulations could have 120
C130 loads, 20 C17 loads and 8 ship loads).
The loads are transported from one or more ports, and aircraft possibly
have to land and refuel on route depending on distances and loads.
Ships only have one load, and then they effectively disappear. Whereas
aircraft fly back and forth transporting loads.
At each port there are several variables, like gang/handler numbers,
loading bays/berths, aircraft handling equipment/ cranes, etc...
The start-lift/ships work day and night but with a limited number of
aircrew (that need resting ever so often). Loading/offloading times
depend of the size of the load and need a free (and rested) gang or AC
handler team to do this.


One question of the simulation would be: "What is the optimal number
of gangs/AC handlers and aircrew ratio (number of aircrews to aircraft)
to move everything in the fasted time possible?"

Thanks again.
Chris
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Randy Poe
science forum Guru


Joined: 24 Mar 2005
Posts: 2485

PostPosted: Thu Jul 13, 2006 4:52 pm    Post subject: Re: Military logistic problem Reply with quote

Keith A. Lewis wrote:
Quote:
christriddle@googlemail.com writes in article <1152780628.774496.282650@b28g2000cwb.googlegroups.com> dated 13 Jul 2006 01:50:28 -0700:
First of all I'm not sure if this belongs here, if not, could you
suggest a more appropriate group.

I'm having some problems researching the possibility of explicit
solutions to military logistics problems.

This falls in the field of "Operations Research" aka OR, so I have added
sci.op-research to the newsgroups list.

To which I'll add that if you can search the Ops Research literature,
particularly the journal "Operations Research", you'll likely find
a wealth of approaches to logistical problems.

- Randy
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Paul A. Rubin
science forum beginner


Joined: 02 Aug 2005
Posts: 5

PostPosted: Thu Jul 13, 2006 3:48 pm    Post subject: Re: Military logistic problem Reply with quote

Keith A. Lewis wrote:
Quote:
christriddle@googlemail.com writes in article <1152780628.774496.282650@b28g2000cwb.googlegroups.com> dated 13 Jul 2006 01:50:28 -0700:
Although, I think the actual problem is more general. I have a
time-step simulation tool that simulates strategic-lift (aircraft,
ships, etc...) moving "stuff" from a start port to an end port.
Obviously aircraft make many flights back and forth.

While a time-step simulation suits this problem, it is quite expensive
in time.
The question I need answering is whether there exists an explicit
solution to such a problem. I'm pretty sure it's not linear, and
perhaps chaotic behaviour prevents such a solution.

By the way, when I say solution I mean things like finding:
a) How long it takes to move everything with various amounts of
start-lift, port infrastructure (#berths, #AC handlers, etc...) and so
on;
b) The optimum number of the above to produce the quickest time; etc...

I would be very grateful if you could point me in a direction to find
if such a thing is possible and if so, whether the complexity of such a
solution would make it impractical.

Many many thanks. Sorry the question is so long (and most probably
confusing!)
Chris Riddle

You have not indicated whether your simulation is stochastic or
deterministic. If the problem is deterministic (or you're willing to
pretend it is), you can likely achieve what you want with a linear
program, mixed integer linear program, or possibly network program.
Transport problems tend to be (plausibly) linear in terms of things like
time, fuel consumption, etc., and in the absence of "wrinkles" that gets
you network model (easily solvable even in quite large instances) or at
worst a linear program (also easily solvable). If you run into things
like fixed-charge issues (we can use port X, but only if we pay a lease
fee that is not proportional to our usage, or truckload v. LTL
shipping), or either-or sorts of constraints (either we use sealift or
we use airlift, but not both), then integer variables enter the picture
and solution times go up.

Sorry, can't be more specific without more detail on the problem.

/Paul
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Keith A. Lewis
science forum Guru


Joined: 24 Mar 2005
Posts: 478

PostPosted: Thu Jul 13, 2006 3:31 pm    Post subject: Re: Military logistic problem Reply with quote

christriddle@googlemail.com writes in article <1152780628.774496.282650@b28g2000cwb.googlegroups.com> dated 13 Jul 2006 01:50:28 -0700:
Quote:
First of all I'm not sure if this belongs here, if not, could you
suggest a more appropriate group.

I'm having some problems researching the possibility of explicit
solutions to military logistics problems.

This falls in the field of "Operations Research" aka OR, so I have added
sci.op-research to the newsgroups list.

Quote:
Although, I think the actual problem is more general. I have a
time-step simulation tool that simulates strategic-lift (aircraft,
ships, etc...) moving "stuff" from a start port to an end port.
Obviously aircraft make many flights back and forth.

While a time-step simulation suits this problem, it is quite expensive
in time.
The question I need answering is whether there exists an explicit
solution to such a problem. I'm pretty sure it's not linear, and
perhaps chaotic behaviour prevents such a solution.

By the way, when I say solution I mean things like finding:
a) How long it takes to move everything with various amounts of
start-lift, port infrastructure (#berths, #AC handlers, etc...) and so
on;
b) The optimum number of the above to produce the quickest time; etc...

I would be very grateful if you could point me in a direction to find
if such a thing is possible and if so, whether the complexity of such a
solution would make it impractical.

Many many thanks. Sorry the question is so long (and most probably
confusing!)
Chris Riddle

For a less compute-intensive solution, figure out where the smallest
bottleneck in the system is, and plan to fill it just under 100%. I
apologize if I'm oversimplifying.

--Keith Lewis klewis {at} mitre.org
The above may not (yet) represent the opinions of my employer.
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christriddle@googlemail.c
science forum beginner


Joined: 10 Jul 2006
Posts: 12

PostPosted: Thu Jul 13, 2006 8:50 am    Post subject: Military logistic problem Reply with quote

Hi,

First of all I'm not sure if this belongs here, if not, could you
suggest a more appropriate group.

I'm having some problems researching the possibility of explicit
solutions to military logistics problems.

Although, I think the actual problem is more general. I have a
time-step simulation tool that simulates strategic-lift (aircraft,
ships, etc...) moving "stuff" from a start port to an end port.
Obviously aircraft make many flights back and forth.

While a time-step simulation suits this problem, it is quite expensive
in time.
The question I need answering is whether there exists an explicit
solution to such a problem. I'm pretty sure it's not linear, and
perhaps chaotic behaviour prevents such a solution.

By the way, when I say solution I mean things like finding:
a) How long it takes to move everything with various amounts of
start-lift, port infrastructure (#berths, #AC handlers, etc...) and so
on;
b) The optimum number of the above to produce the quickest time; etc...

I would be very grateful if you could point me in a direction to find
if such a thing is possible and if so, whether the complexity of such a
solution would make it impractical.

Many many thanks. Sorry the question is so long (and most probably
confusing!)
Chris Riddle
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