Designing Coupled Engineered Systems Under Uncertainty

The evolving technology and state of art research have provided various platforms for transforming engineering design by merging product and process design with materials. This merger gives us an extended design space and a larger search space with a potential benefit of discovering engineering solutions that include better-quality product without compromising performances. The opportunities also pose serious challenges. The realization and modeling of the extended design space in itself is very complex as result of numerous interacting decisions (coupled decisions) at varying levels of priority. With a plethora of materials and manufacturing processes to choose from, the need for decision support to aid designers to efficiently explore the design space becomes imperative. Furthermore, the uncertainty that lies at each stage of decision making need to be properly addressed to render the effectiveness and accuracy of the undertaken decisions. The design of engineered systems, in context of this thesis, is viewed from the Decision-Based Design (DBD) perspective. In Decision-Based Design (DBD), the principal role of a human designer is to make decisions and engineering design is recognized as a decision- making process. The implementation of Decision-Based Design can take many forms, one manifestation of the Decision-Based Design (DBD) construct is the Decision Support Problem Technique (DSPT) developed to provide support to human designers in exercising judgment in making design decisions. All decisions identified in the DSPT are categorized as selection, compromise, or a combination of these. Selection decisions are modeled as selection Decision Support Problems (sDSP) and the compromise decisions are modeled as compromise Decision Support Problems (cDSP). In this thesis, a framework for modeling design decisions involving multiple interacting decisions, called the Multilevel Decision Scenario Matrix (MDSM) is proposed. The decision pattern pertaining to several interacting decisions is identified for a given engineering design problem using MDSM and a mathematical formulation with robustness metrics is implemented for the identified decision pattern to explore decisions that are relatively insensitive to uncertainties. Then, a generic robust decision method, based on compromise Decision Support Problem Construct is proposed. The integration of coupled decisions with robustness metrics, specifically, Design Capability Index (DCI) and Error Margin Index (EMI) is detailed as a method for designing engineered systems under uncertainty. The proposed method is applied in designing of fender, one-stage reduction gearbox and, composite structures

A method for robust design in a coupled decision environment

The design of a connected engineered system requires numerous design decisions that influence one another. In a connected system that comprises numerous interacting decisions involving concurrency and hierarchy, accounting for interactions while also managing uncertainties, it is imperative to make robust decisions. In this article, we present a method for robust design using coupled decisions to identify design decisions that are relatively insensitive to uncertainties. To account for the influence among decisions, design decisions are modelled as coupled decisions. They are defined using three criteria: the types of decisions, the strength of interactions and the decision levels. In order to make robust decisions, robust design methods are classified based on sources of uncertainty, namely, Type I (noise factors), Type II (design variables) and Type III (function relationship between design variables and responses). The design of a one-stage reduction gearbox is used as a demonstration example. To illustrate the proposed method for robust design using coupled decisions, we present the simultaneous selection of gear material and gearbox geometry in a coupled decision environment while managing the uncertainties involved in designing gearboxes.Ye

Woody Plant Encroachment Impacts on Groundwater Recharge: A Review

Woody plant encroachment has profound impacts on the sustainable management of water resources in water-limited ecosystems. However, our understanding of the effects of this global phenomenon on groundwater recharge at local and regional scales is limited. Here, we reviewed studies related to (i) recharge estimation methods; (ii) mechanisms by which woody plants impact groundwater recharge; (iii) impacts of woody plant on recharge across different soil and geology; (iv) hydrological repercussions of woody plant removal; and (v) research gaps and needs for groundwater studies. We identified six different methods: water balance, water table, isotopes, chloride mass balance, electrical geophysical imaging, and modeling were used to study the impact of woody encroachment on groundwater. Woody plant encroachment could alter soil infiltration rates, soil water storage, transpiration, interception, and subsurface pathways to affect groundwater recharge. The impact is highly variable, with the extent and the magnitude varying across the soil, substrate, plant cover, and topographic locations. Our review revealed mixed effects of woody plant removal on groundwater recharge. Studies of litter interception, root water uptake, soil moisture dynamics, and deep percolation along with the progression of woody plant encroachment are still limited, warranting further experimental studies focusing on groundwater recharge. Overall, information about woody plant encroachment impacts on groundwater resources across a range of scales is essential for long-range planning of water resources