arXiv subjects

Gregory Mocko

Publications and source records attributed to Gregory Mocko.

5 recordsLinked to original sources

arXiv2025

Comparative Model Fidelity Evaluation to Support Design Decisions for Complex, Novel Systems of Systems

Systems design processes are increasingly reliant on simulation models to inform design decisions. A pervasive issue within the systems engineering community is trusting in the models used to make decisions about complex systems. This work presents a method of evaluating the trustworthiness of a model to provide utility to a designer making a decision within a design process. Trusting the results of a model is especially important in design processes where the system is complex, novel, or displays emergent phenomena. Additionally, systems that are in the pre-prototype stages of development often do not have sources of ground truth for validating the models. Developing methods of model validation and trust that do not require real-world data is a key challenge facing systems engineers. Model fidelity in this work refers to the adherence of a model to real-world physics and is closely tied to model trust and model validity. Trust and validity directly support a designer's ability to make decisions using physics-based models. The physics that are captured in a model and the complexity of the mathematical representation of the physics contribute to a model's fidelity, and this work leverages the included physical phenomena to develop a means of selecting the most appropriate for a given design decision.

cs.CE↗

arXiv2025

Axioms for Model Fidelity Evaluation

Digital engineering has transformed the design and development process. However, the utility of digital engineering is fundamentally dependent on the assumption that a simulation provides information consistent with reality. This relationship is described as model fidelity. Despite the widespread use of the term, existing definitions of model fidelity often lack formal rigor in practical application, which leaves ambiguity in how this similarity should be evaluated. This paper presents seven fundamental axioms to aid the development of future fidelity evaluation frameworks. An example of a ground vehicle model is used under an existing fidelity evaluation framework to observe the applicability of these axioms. In addition, these axioms are used as a reference point for considering future opportunities in future work related to model fidelity.

cs.CE↗

arXiv2025

Constraint Hypergraphs as a Unifying Framework for Digital Twins

Digital twins, used to represent physical systems, have been lauded as tools for understanding reality. Complex system behavior is typically captured in domain-specific models crafted by subject experts. Contemporary methods for employing models in a digital twin require prescriptive interfaces, resulting in twins that are difficult to connect, redeploy, and modify. The limited interoperability of these twins has prompted calls for a universal framework enabling observability across model aggregations. Here we show how a new mathematical formalism called a constraint hypergraph addresses these challenges in interoperability. A digital twin is shown to be the second of two coupled systems where both adhere to the same constraint hypergraph, permitting the properties of the first to be observable from the second. Interoperability is given by deconstructing models into a structure enabling autonomous, white-box simulation of system properties. The resulting digital twins can interact immediately with both human and autonomous agents. This is demonstrated in a case study of a microgrid, showing how both measured and simulated data from the aggregated twins can be provided regardless of the operating environment. By connecting models, constraint hypergraphs supply scientists and modelers robust means to capture, communicate, and combine digital twins across all fields of study. We expect this framework to expand the use of digital twins, enriching scientific insights and collaborations by providing a structure for characterizing complex systems.

eess.SY↗

arXiv2021

Optimal Pacing of a Cyclist in a Time Trial Based on Individualized Models of Fatigue and Recovery

This paper formulates optimal pacing of a cyclist on hilly terrain time-trials as a minimum-time optimal control problem. Maximal power of a cyclist serves as a time-varying constraint and depends on fatigue and recovery which are captured via dynamic models proposed early in the paper. Experimental protocols for identifying the individualized parameters of the proposed fatigue and recovery models are detailed and results for six human subjects are shown. In an analytical treatment via necessary conditions of Pontryagin Minimum Principle, we show that the cyclist's optimal power in a time-trial is limited to only four modes of all-out, coasting, pedaling at a critical power, or constant speed (bang-singular-bang). To determine when to switch between these modes, we resort to numerical solution via dynamic programming. One of the subjects is then simulated on four courses including the 2019 Duathlon National Championship in Greenville, SC. The dynamic programming simulation results show 24% reduction in travel time over experimental results of the self-paced subject who is a competitive amateur cyclist. The paper concludes with description of a pilot lab experiment in which the subject trial time was reduced by 3% when the near-optimal pace was communicated to her in real-time.

eess.SY↗

arXiv2020

Experimental Modeling of Cyclists Fatigue and Recovery Dynamics Enabling Optimal Pacing in a Time Trial

Improving a cyclist performance during a time-trial effort has been a challenge for sport scientists for several decades. There has been a lot of work on understanding the physiological concepts behind it. The concepts of Critical Power (CP) and Anaerobic Work Capacity (AWC) have been discussed often in recent cycling performance related articles. CP is a power that can be maintained by a cyclist for a long time; meaning pedaling at or below this limit, theoretically, can be continued for infinite amount of time. However, there is a limited source of energy for generating power above CP. This limited energy source is AWC. After burning energy from this tank, a cyclist can recover some by pedaling below CP. In this paper we utilize the concepts of CP and AWC to mathematically model muscle fatigue and recovery of a cyclist. Then, the models are used to formulate an optimal control problem for a time trial effort on a 10.3 km course located in Greenville SC. The course is simulated in a laboratory environment using a CompuTrainer. At the end, the optimal simulation results are compared to the performance of one subject on CompuTrainer.

math.OC↗