Transport companies often have a published timetable. To maintain timetable reliability despite d... more Transport companies often have a published timetable. To maintain timetable reliability despite delays, companies include buffer times during timetable development and adjust the traveling speed during timetable execution. We develop an approach that integrates timetable development and execution. We model execution of the timetable as a stochastic dynamic program (SDP). An SDP is a natural framework to model random events causing (additional) delay, propagation of delays, and real-time optimal speed adjustments. However, SDPs alone cannot incorporate the buffer allocation during timetable development, as buffer allocation requires choosing the same action in different states of the SDP. Motivated by the practical need for timetables that operate well during timetable execution, our model seeks the buffer allocation that yields the SDP that has minimal long-run average costs. We derive several analytical insights into the model. We prove that costs are joint convex in the buffer tim...
This paper gives an overview of scientific literature that describes and discusses cases of rever... more This paper gives an overview of scientific literature that describes and discusses cases of reverse logistics activities in practice. Over sixty case studies are considered. Based on these studies we are able to indicate critical factors for the practice of reverse logistics. In addition we compare practice with theoretical models and point out research opportunities in the field
This paper gives an overview of scientific literature that describes and discusses cases of rever... more This paper gives an overview of scientific literature that describes and discusses cases of reverse logistics activities in practice. Over sixty case studies are considered. Based on these studies we are able to indicate critical factors for the practice of reverse logistics. In addition we compare practice with theoretical models and point out research opportunities in the field.
In this report we discuss a model that can be used to determine stocking levels using the data th... more In this report we discuss a model that can be used to determine stocking levels using the data that comes forward from a Shell RCM analysis and the data available in E-SPIR. The model is appropriate to determine stock quantities for parts that are used in redundancy situations, and for parts that are used in different pieces of equipment with different downtime costs. Estimating the annual production loss using the model consists of a number of steps. First, we need to determine which spares are used for the repairs of which failure modes. In the second step, we estimate the average waiting time for spares as a function of the number of spares stocked. In the third step, the annual downtime costs are determined. We combine the downtime costs with the holding costs to determine the optimal number of parts to stock.
Transport companies often have a published timetable. To maintain timetable reliability despite d... more Transport companies often have a published timetable. To maintain timetable reliability despite delays, companies include buffer times during timetable development and adjust the traveling speed during timetable execution. We develop an approach that integrates timetable development and execution. We model execution of the timetable as a stochastic dynamic program (SDP). An SDP is a natural framework to model random events causing (additional) delay, propagation of delays, and real-time optimal speed adjustments. However, SDPs alone cannot incorporate the buffer allocation during timetable development, as buffer allocation requires choosing the same action in different states of the SDP. Motivated by the practical need for timetables that operate well during timetable execution, our model seeks the buffer allocation that yields the SDP that has minimal long-run average costs. We derive several analytical insights into the model. We prove that costs are joint convex in the buffer tim...
This paper gives an overview of scientific literature that describes and discusses cases of rever... more This paper gives an overview of scientific literature that describes and discusses cases of reverse logistics activities in practice. Over sixty case studies are considered. Based on these studies we are able to indicate critical factors for the practice of reverse logistics. In addition we compare practice with theoretical models and point out research opportunities in the field
This paper gives an overview of scientific literature that describes and discusses cases of rever... more This paper gives an overview of scientific literature that describes and discusses cases of reverse logistics activities in practice. Over sixty case studies are considered. Based on these studies we are able to indicate critical factors for the practice of reverse logistics. In addition we compare practice with theoretical models and point out research opportunities in the field.
In this report we discuss a model that can be used to determine stocking levels using the data th... more In this report we discuss a model that can be used to determine stocking levels using the data that comes forward from a Shell RCM analysis and the data available in E-SPIR. The model is appropriate to determine stock quantities for parts that are used in redundancy situations, and for parts that are used in different pieces of equipment with different downtime costs. Estimating the annual production loss using the model consists of a number of steps. First, we need to determine which spares are used for the repairs of which failure modes. In the second step, we estimate the average waiting time for spares as a function of the number of spares stocked. In the third step, the annual downtime costs are determined. We combine the downtime costs with the holding costs to determine the optimal number of parts to stock.
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Papers by Rommert Dekker