05-02-2013, 02:18 PM
Maintenance optimization at VAC
Maintenance optimization.ppt (Size: 901.5 KB / Downloads: 41)
Maintenance activities at VAC
Volvo Aero Corp. (VAC), Trollhättan
Aircraft engines; 3 billion SEK (2004)
Military and civil maintenance
Fuel prices while operators compete with prices
VAC improves competition by enabling an effective cost reduction
Costs: # maintenance occasions; material (spare parts) and work costs
Opportunistic/preventive maintenance necessary!
More on fixed costs
Maintenance of an engine can take up to 50 days
Often reserve engines are used (are kept in store), especially in civil operations
Each maintenance operation incurs a huge cost: administration, extensive testing, incl. probing and infrared measurements; staff intensive
Logic
Two types of components: safety-critical ones–life times determined at Solid Mechanics; others are ”on condition”; replaced if broken
OC parts responsible for 30% of maint. occasions
Life measured in ”cycles” – monitored extensively especially in military aircraft
Engine composed of modules; individually shipped to VAC; simple maintenance done at some military sites
Large civil airlines perform their own maintenance
Current maintenance depend on cycles left and a measure of ”remaining value”
Notes on the integer program
The basic model (without additional spare parts – see below) is quite special:
1. The x variables can be assumed to be continuous – for fixed binary z values the problem has the integrality property! (coefficient matrix totally unimodular)
2. All the constraints define facets of the convex hull of the feasible set – a strong formulation, and therefore (probably) relatively easy to solve!
The above is no longer true for more general problems with work costs and spare parts included
Current policy
Value policy: introduce a cost per time measure:
If is the remaining life of part i its value is the product of these two values
Value policy: compare value with fixed cost d; replace if value is less
Problem: cheap parts are always replaced; remedy: include a minimum time between replacements for cheap parts – often a requirement from clients