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In addition there are constraints governing the assignment of specific fleets to specific legs in the flight schedule.


In addition there are constraints governing the assignment of specific fleets to specific legs in the flight schedule.
In addition there are constraints governing the assignment of specific fleets to specific legs in the flight schedule.
There are also constraints relating to the availability of aircraft in the different fleets, regulations governing crew assignments, scheduled maintenance requirements, and airport restrictions.
As the reader can imagine, the task of gathering and maintaining the information required to mathematically specify all of these is in itself a tremendous task.
While building such a model is difficult but not impossible, the ability to solve it to optimality was impossible until the very recent past.
However, computational O.
has developed to the point that it is now feasible to solve such complex models; the system at Delta is called Coldstart and uses highly sophisticated implementations of linear and integer programming solvers.Fassilia
United States. Alabama



day: 19.09.2018
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In addition there are constraints governing the assignment of specific fleets to specific legs in the flight schedule.

In order to avoid this problem, the company had to suspend production over the weekends and replace worn-out tools or oc
In order to avoid this problem, the company had to suspend production over the weekends and replace worn-out tools or occasionally use overtime to get back on schedule.
The key point to note from this application is that a simulation model could be used to analyze a highly complex system for a number of what-if scenarios and to gain a better understanding of the dynamics of the system.
The problem is modeled by a very large mixed-integer linear program - a typical formulation could result in about 60,000 variables and 40,000 constraints.
The planning horizon for each problem is one day since the assumption is made that the same schedule is repeated each day exceptions such as weekend schedules are handled separately .
The primary objective of the problem is to minimize the sum of operating costs including such things as crew cost, fuel cost and landing fees and costs from lost passenger revenues.
The bulk of the constraints are structural in nature and result from modeling the conservation of flow of aircraft from the different fleets to different locations around the system at different scheduled arrival and departure times.Fassilia
United States. Alabama



day: 19.09.2018
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In addition there are constraints governing the assignment of specific fleets to specific legs in the flight schedule.

It was also determined that minimizing the makespan which is the time required to produce all daily requirements would b
It was also determined that minimizing the makespan which is the time required to produce all daily requirements would be the best objective since this would also maximize as well as balance machine utilization.
A detailed simulation model was then constructed using a specialized language called SLAM.
In addition to the process plans required to specify the actual machining of the various part types, this model also accounted for a number of factors such as material handling, tool handling and fixturing.
Several alternatives were then simulated to observe how the system would perform and it was determined that a fairly simple set of heuristic scheduling rules could yield near optimal schedules for which the machine utilizations were almost 85 .
However, what was more interesting was that this study also showed that the stability of the schedule was strongly dependent on the efficiency with which the cutting tools used by the machines could be managed.
In fact, as tool quality starts to deteriorate the system starts to get more and more unstable and the schedule starts to fall behind due dates.Fassilia
United States. Alabama



day: 19.09.2018
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StarBlend is an extension of OMEGA to a multi-period planning environment where optimal decisions could be made over a l
StarBlend is an extension of OMEGA to a multi-period planning environment where optimal decisions could be made over a longer planning horizon as opposed to a single period.
In addition to blend quality constraints, the optimization model also incorporates inventory and material balance constraints for each period in the planning horizon.
The optimizer uses an algebraic modeling language called GAMS and a nonlinear solver called MINOS, along with a relational database system for managing data.
The whole system resides within a user-friendly interface and in addition to immediate blend planning it can also be used to analyze various what-if scenarios for the future and for long-term planning.
At Caterpillar, a preliminary analysis showed that the FMS was being underutilized and the objective of the project was to define a good production schedule that would improve utilization and free up more time to produce additional parts.
In the orientation phase it was determined that the environment was much too complex to represent it accurately through a mathematical model, and therefore simulation was selected as an alternative modeling approach.Fassilia
United States. Alabama



day: 19.09.2018
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It works by breaking up the overall problem into smaller, more manageable problems by using a heuristic decomposition ap
It works by breaking up the overall problem into smaller, more manageable problems by using a heuristic decomposition approach.
Mathematical models within the problem are solved using linear programming along with concepts from material requirements planning.
The entire system interfaces with sophisticated databases allowing for forecasting, quotation and order entry, materials and dynamic information on capacities.
Harris estimates that this system has increased on-time deliveries from 75 to 95 with no increase in inventories, helped it move from 75 million in losses to 40 million in profits annually, and allowed it to plan its capital investments more efficiently.
As an initial response to this complex problem, in the early to mid 1980 s Texaco developed a system called OMEGA.
At the heart of this was a nonlinear optimization model which supported an interactive decision support system for optimally blending gasoline; this system alone was estimated to have saved Texaco about 30 million annually.Fassilia
United States. Alabama



day: 19.09.2018
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