Control Policies for a Water-Treatment System Using the Markov Decision Process. Part 2: Simulation and Analysis

Abstract

This article is the second part of a two-part research study of a theoretical water-treatment system based on the NASA Baseline Values and Assumptions Document (BVAD) [7]. It focuses on the decisionmaking model created to choose the "best" policy to be applied to the water-treatment system based on hourly system conditions. Due to the resemblance between the behavior of this system and the Markovian process, this system is constructed based on the Markovian model. The water system consists of two subsystems: a hygiene-water subsystem that supplies water for laundry, urinal fl ush, dish wash, oral hygiene and shower; and a potable-water subsystem that supplies water for drinking and food rehydration. In order to assess the conditions of the water system, various aspects of the system, such as hourly and accumulated water defi ciency, and amount of clean water available for use, are captured on an hourly basis. A baseline policy and policies derived from it are tested to fi nd the best policy for the system to operate under the most economical conditions while providing enough clean water for crew consumption. The best policy is obtained through various mathematical modeling techniques. Outcomes are compared against a system that uses the baseline policy. Results show that an intuitively "good" policy may not always be the best policy for the system. The system performance is measured in terms of a reward value, which is assigned based on the system conditions.

Risk analysis methods of water supply systems: comprehensive review from source to tap

“…This would enormously facilitate the work of managers and operators in terms of repair, maintenance and budgetary constraints. Chiam, Yih, and Mitchell (2009) applied a control policy for a water facility system using the Markov decision process. Different systemic factors such as water shortages/cuts, lack of storage supply and how much water can be used or collected in a certain period of time (one hour in this case).…”

Aportación a la implantación del análisis de riesgo en los sistemas de distribución del agua: caso del Cryptosporidium para distintos niveles de desarrollo tecnológico en la potabilizadora

“…En este estudio de caso, los resultados se compararon con un sistema que utilizaba la política básica. Los resultados señalan que el juicio personal y lo que "parece correcto" no es necesariamente beneficioso para el sistema (Chiam et al, 2009).…”