Development of a Three-Dimensional Scripted Human Thermoregulation Model Framework for the Lower Limb

Computational modeling of complex physiological systems has become a crucial focus in the realm of engineering modeling and simulation. One complex physiological response to be accurately modeled is thermoregulation, which engages several systems within the human body, such as the cardiovascular, muscular, and integumentary systems. For spaceflight, thermoregulation is of particular interest for the design of life-support systems, spacecraft habitats, and spacesuits. Thermoregulation requires passive and active contributions. Passive considerations include body composition (anthropometry, gender, age, anatomy) and environmental interactions while active considerations include vasomotor response, sweating, and shivering. Human thermoregulation models, including the 41-Node Man (METMAN) and the Wissler model, have been applied to human spaceflight since the 1960s. However, they consider thermal variations in only one or two dimensions and are generally limited to standalone programs (e.g., written in Fortran) without a commercial software interface. This current research considers a new framework for modeling human thermoregulation through scripting of commercial thermal analysis software. Specifically, Thermal Desktop (C&R Technologies) is selected for this framework due to its application programming interface (API), OpenTD, that allows automation of its fluid flow and radiation implementation modules. The framework supports three-dimensional thermal modeling with variable anthropometry. The baseline model presented in this work focuses on the lower limb. Two segments are modeled as tapered cylinders to represent the thigh and lower leg, and their composition includes bone, muscle, fat, and skin with physical and thermal properties defined from well-established human thermal models. For the baseline model, heat rejection from the body focuses on the passive human thermoregulation system through conduction, convection, and radiation only. Verification of this model is conducted against analytical examples along with existing human thermal models previously mentioned, and its relative performance is discussed.