MORPHEUS : Modelica-based implementation of a numerical human model involving individual human aspects

Wölki, Daniel; van Treeck, Christoph Alban (Thesis advisor); Hensen, Jan (Thesis advisor)

Aachen (2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2017

Abstract

This work introduces a fully scalable numerical multi-element model for the prediction of the humanthermoregulatory responses of individuals to static, dynamic, homogeneous and inhomogeneousphysical ambient conditions. The described Morphable Human Energy Simulator (MORPHEUS)is based on the mathematical structure of the well-known Fiala model (Fiala et al., 1999, 2001)and was combined with modeling ideas of Tanabe et al. (2002). It is implemented in the acausal,equation-based modeling language Modelica and used in connection with the commercial codeinterpreterDymola. The latter facilitates the export of the model as a functional mock-up unit(FMU) for co-simulation, thus enabling its use within real-time applications.An extensive literature research is shown. It gives an overview of currently existing numericalhuman models, their fields of application, individualization approaches and key parameters thatinfluence the human thermoregulatory response.The implemented numerical human model, MORPHEUS, follows a component-based modeling approach,which offers the advantages of code-reusability and component substitutability/-extensibilitywithout having to modify the entire system of equations. It models the heat transfer phenomenaat the surface of the human body (mixed convection, longwave radiation, skin-moisture evaporationand diffusion for individual body segments) as well as heat transfer mechanisms that occurinside living tissue (blood circulation, heat production, -conduction and -storage). Furthermore,it considers the non-uniform thermal and evaporative resistance of clothing as well as influencesof the body posture on the radiative heat exchange between the human body and its surroundingstructures.The anatomical part of a human being is approximated with cylindrical and spherical elements andmodeled within the Passive System (PS) component. It includes a total of seven different tissuematerials and models the dry and wet heat exchange of the human being with the environmentrelated to the respiratory tract. The active control mechanisms that aim to keep the body coretemperature on a nearly constant level (37 C) are modeled within an Active System (AS) component.The latter follows a temperature error signal approach that involves skin and hypothalamustemperatures as the afferent signals that trigger the dynamic thermoregulatory responses shivering,sweating, vasoconstriction and vasodilatation. The entire system in its standard configuration(Fiala et al., 1999, 2001) was verified with literature data and shows good agreement with thecorresponding publication results.Extensive body composition data of female and male persons aged between 18 to 35 years arepresented. They were statistically evaluated and served as the base for the attached numerical representationsof a typical female subject (TFS) and a typical male subject (TMS). The latter wereused to demonstrate the scalability of the model as well as to theoretically investigate the genderspecificdifferences in the thermoregulatory response related to differences in body composition.The corresponding data were collected during diverse experiments and comprise detailed in-vivomeasurements of 289 subjects (168 males, 121 females) for the extremities and the trunk section. Inthis regard, a technology review of different body composition measurement technologies is introduced.It revealed multi-frequency bioelectrical impedance analysis (BIA) as the method of choicebecause of its accuracy, cost-effectiveness, flexibility with respect to location and manageability.Two different ways of adapting the passive model part of MORPHEUS to the anatomical characteristicsof individuals are shown. The latter comprise the modification of individual tissuecharacteristics (e.g. basal metabolic rate, density, etc.) as well as the geometrical adaptation oftissue layer thicknesses in combination with the scaling of segmental lengths. The former, however,does not reflect reality and cannot be used in connection with the realistic modeling of the humananatomy. In this regard, a systematized adaptation procedure is presented, which can be used forthe automatized adaptation of the PS-component.The real-time applicability of MORPHEUS is demonstrated on the base of the introduced humancenteredclosed-loop control (HCCLC) concept. In this regard, the model serves as a virtual humantwo-point controller of a thermoelectric thermostat that was used to control the indoor operativetemperature of an office room over a period of four consecutive office days in December 2016 inAachen, Germany. As a control signal for the thermostat the predicted mean skin temperature ofMORPHEUS configured with the parameters originally suggested by Fiala et al. (1999) was used(threshold value for thermal neutrality 34 C). Here, values bigger than the predefined thresholdcaused a deactivation of the radiator and vice versa. In addition, the thermoregulatory responsesof MORPHEUS configured with the anatomical characteristics of the TFS were simulated in parallel.Its corresponding reactions were chosen to have no influence on the thermostat. However, thepredicted radiator states were recorded, too. The results of the experiment demonstrate a realisticinteraction between the humanoids, the building and the outdoor climate. Furthermore, they indicategender-specific differences in heat requirements and show the need for customizable Heating,Ventilation and Air Conditioning (HVAC) systems that act locally on the human body, in orderto save energy and to be able to provide comfortable thermal environments for individuals. A firstcomparison with published literature data confirms these findings. A validation of the outcomeswith subject experiments, however, must be part of future work.