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Takao Itami (Software Cradle, Software Engineering Dept.)
Thermoregulation Model JOS Function

 

Software Cradle's SC/Tetra thermo-fluid analysis software includes the JOS function which is used to simulate and analyze human body skin surface temperature and quantity of perspiration. SC/Tetra divides a model of the human body into 17 segments and simulates the morphological and physiological characteristics and thermoregulation function of each segment by solving heat balance equations. "The comfort of human beings will vary depending on the environment. SC/Tetra can be used to analyze the human response which will help engineers design better products," says Mr. Itami, the developer of the JOS and a member of the Software Cradle Co., Ltd staffs. In this article, Mr. Itami tells the story behind the development of the JOS function in SC/Tetra.

Takao Itami
Software Cradle, Co., Ltd.
Tokyo Branch, Software Engineering Dept.

Figure 3: Heat transfer in the human body using JOS model
(click to enlarge)

How Did User Feedback Affect Development of the JOS Model?

 Professor Tanabe, the developer of the JOS model, helped and supported us. His laboratory uses SC/Tetra, so that was also a tremendous benefit. He gave us valuable input about selecting JOS conditions and how to input clothing conditions. Our relationship with the laboratory is very special. The laboratory developed the JOS model but was also an SC/Tetra user. In addition, Professor Shiraishi at the University of Kitakyusyu requested a calculation function for skin temperature. At that time, the JOS model calculated body temperature for each of the 17 segments. But Professor Shiraishi proposed calculating the skin temperature separate from the body temperature. He felt this was necessary to accurately calculate a condition such as the skin face temperature when the air conditioned air is blowing on it. Consequently, we improved the JOS function so it calculates the skin temperature at each mesh point in the body segment.

Why Did you Adopt a Pull-down Menu GUI?

 The JOS inputs are a set of parameters (age, sex, body fat rate, and clothing) and geometry. These parameters use input boxes and buttons to define their respective values. For geometry, especially body segment information, we wondered which input approach would be the most user-friendly. Initially we used a method where the user selected regions from a list of region names and defined the position of each region. However, the developers of our SC/Tetra preprocessor suggested using a pull-down menu. While this method is not as easy to use as we would like, we adopted it because the resultant GUI was simple and clear.

What are the Best Features of SC/Tetra JOS?

 The SC/Tetra JOS function has four human body postures. The user can start an analysis using predefined human body shape data. Four different clothes conditions are available courtesy of actual measurements from Professor Tanabe. JOS is a user-friendly for engineers, designers, and developers.
 

Please Describe How the JOS Function is a Used in SC/Tetra

 The JOS function requires setting physiological parameters such as age, sex, and body fat rate, clothes conditions, body surface area (indicating body size), and position information of body segments (head and neck). The body surface area is automatically determined from the selected human body shape. Hence, the user does not need to provide any surface area information. All the other input parameters can be set in one dialog.

 To use the JOS function, the user prepares the human body analysis model as previously described. Then the environmental conditions (humidity, air flow, and temperature) are set. When a new human body condition is created in the JOS dialog, the surface of the human body is treated as a static wall. This means that wall conditions do not need to be specified. If radiation is a factor, the emissivity of the human skin must be defined.
 

 When the calculations are complete, skin temperature and skin wittedness are output to the SC/Tetra FLD file. Skin wittedness is an index that indicates level of perspiration. The SC/Tetra calculation log le contains other pertinent information such as core and temperature of the blood pool, which are thermoregulation parameters. This information can be viewed as text or visualized through the SC/Tetra's postprocessor.
 

Do you Have Any Special Advice to Give to JOS Function Users?

 The JOS function assumes water vapor generated by sweating evaporates completely. Therefore the function is not suitable for analyzing a person who is soaked in sweat. In addition, excessively high temperature and high humidity environments, such as that found in a sauna, should be avoided. The human body is greatly affected by upward flow generated by the body temperature. Buoyancy should be considered in the analysis unless other strong convective forces are present, e.g. extremely strong winds.
 

 The entire surface of the human body being simulated must be contained within the SC/Tetra's computational domain to properly interface with the surrounding environment. If a part of the body surface contacts the boundaries of the computation domain, the conditions at that point cannot be calculated. In addition, sensible or latent heat through a body surface cannot be calculated. Therefore, when analyzing a human body standing on a floor, a solid mesh must be generated inside the floor.

Figure 4: Thermal environment analysis of a coach showing the
​contour of human body surface (click to enlarge)

Closing Remarks

 The JOS function in SC/Tetra enables simulation of human body temperature and amount of perspiration for a given environment. Model set-up is easily achieved using predefined human body shape data. Being able to assess human body thermal comfort using computational simulation, especially with the easy set-up found in SC/Tetra JOS, provides substantial benefits compared to obtaining this same information experimentally. A thermal mannequin costs more than 10 million yen (over $100,000 USD). Experiments using several thermal mannequins (e.g. many passengers in a tour bus) will be unrealistically expensive. In contrast, the SC/Tetra JOS function can perform this calculation routinely with any number of passengers. The next step is to calculate a true comfort index from the body temperature and perspiration outputs currently generated. We appreciate any comments and requests from our customers.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of November 28, 2013 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

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