On the advantage of assuming constant mass flow rates in discretized dynamic material flow models

Abstract

When using discrete dynamic stock models in combination with lifetime distributions, the total amount of material transported in a period is implicitly assumed to be a spike at either the start or the end of the considered period. Depending on the choice, the residence time of materials in stock is either underestimated in the inflow-at-start approach or overestimated in the inflow-at-end approach. This paper proposes to solve this assignment problem by assuming the total mass flow to be evenly distributed over the period, using a continuous dynamic stock model, and discretizing the results afterward. It will be shown that this so-called uniform-inflow approach delivers more realistic results.