Scheduling

Scheduling can be defined as the task of assigning activities to limited resources at particular times and thereby to determine an efficient sequence of these activities. In the context of business problems, scheduling is also known as the practice of arranging and optimizing the workload in a specified production or service process. Well known problems are machine scheduling, project scheduling and timetabling.


FLEXIBLE PROJECTS FOR THE CUSTOMER-SPECIFIC REMANUFACTURING OF COMPLEX HIGH-CAPITAL GOODS

Influence of the chosen project structure on profit

For the regeneration of complex capital goods such as aircraft engines, there are different remanufacturing modes available. They can be distinguished by the use of resources, the throughput time and the costs. The choice of a regeneration mode determines the functional properties of the regenerated capital good, such as durability or energy consumption. The requirements on the regeneration processes and results - and thus also on the execution modes to be selected - vary depending on the specific good and customer. For the planning of such processes, the regeneration process can be interpreted as a flexible resource-constrained project, in which the project structure and thus the execution modes are determined model-endogenously.


PLANNING MAINTENANCE PROCESSES OF WIND TURBINES

Maintenance of a wind turbine’s rotor blade (Source: Nordex Group)

Wind turbines are subject to age- and weather-related wear and tear during their service life. Therefore, they must be inspected at fixed intervals and, depending on the condition, be repaired by qualified personnel. The maintenance and repair measures can be implemented in various ways. These so-called regeneration modes differ mainly with regard to organizational aspects. For example, only one team can be deployed, or two teams can work in parallel at one location. The implementation of the regeneration process also depends on the equipment that is available on site. There is a trade-off between lower costs and longer processing times. Next to the spatial dimension, another significant aspect of regeneration planning for wind turbines is the uncertainty of the regeneration processes, which results in particular from the unknown work contents and the weather-dependent accessibility.


TRUCK SCHEDULING IN CROSS-DOCKING-TERMINALS

Schematic layout of a parcel hub

In the parcel service industry, cross-docking terminals are widely used to consolidate parcel flows from different locations. After being unloaded from the inbound trucks, the parcels are transported to the outbound trucks according to their destinations, predominantly using conveyors. In this regard, our research focuses on the scheduling of incoming trucks at the inbound doors. Possible objectives are the minimization of the overall completion time or of the delay of the outbound trucks. In the context of scheduling the inbound trucks, several characteristics of the terminal have to be considered. Important restrictions are conveyor capacities as well as fixed departures of the outbound trucks. First numerical studies show that flexible unloading speeds are a promising option to efficiently use the conveyor capacities.


PLANNING OF ROTOR BLADE MAINTENANCE PROCESSES ON ONSHORE WIND TURBINES

The planning of rotor blade maintenance processes on onshore wind turbines is located in the field of tactical pre-planning. The objective of the project is to reduce the logistics costs for the maintenance of wind turbines, to use existing capacities more efficiently and to increase the availability of wind turbines. The maintenance processes to be scheduled for a season are planned in such a way that  the capacities of the maintenance teams in particular are used in the best possible way, taking into account legal, logistical and technical conditions. Mathematical decision models as well as exact or heuristic solution methods from the field of operations research are used methodically for this purpose.