Thermal simulations show heat challenge for Olympics

Technology News |
By Nick Flaherty

Engineers have used a thermal modelling tool to highlight the challenges of heat for athletes at the Olympics in Toyko, one of the hottest on record

The team from the UK-based Hexagon Manufacturing Intelligence simulated the effects of the hot, humid conditions on a male athlete competing in the 10,000m race (the longest stadium-based track race). The Cradle CFD tool is based on an unstructured mesh to accurately represent complicated geometry and is used by manufacturers such as Airbus, Toyota, and Samsung.

Despite the race taking place after sunset, the simulations show athletes still face gruelling conditions. Even under average conditions of 27 degrees C (80.6 F) and 70 percent humidity, runners of the 10,000m could experience core temperatures of above 39 ºC (102.3 ºF). A temperature of above 38 ºC (100.4 ºF) is considered feverish and research shows that humans need to maintain their core temperature between 35 and 39 ºC (95 and 102.2 ºF) for optimal functioning of biochemical reactions.

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To show how close athletes could come to the detrimental impact of the heat with just a few degrees’ temperature change, the engineers simulated two different scenarios. The first was hotter than average conditions with negligible wind speed, 32 ºC air temperature and 90 percent humidity. The second used average conditions for the time of year: negligible wind speed, 27 ºC air temperature and 70 percent humidity.

The simulations show the considerable impact a slight weather change can make. If the air temperature rises to just five degrees above average, the simulated core temperature increases to 39.77 ºC (103.6 ºF) and skin temperature to 37 ºC (98.6 ºF).

In addition, in the hotter of the two scenarios, athletes’ core head temperature could reach over 40 C (104 ºF), while even in average conditions the head core temperature could be 39.2 ºC (102.6 ºF).

Humidity will also play an important factor in athlete performance and health. Average humidity for Tokyo in July is 70 percent, but if humidity rises to 90 percent athletes will sweat an average of 810ml (almost 1.5 pints), compared to 630ml (approximately 1.3 pints) over the duration of the approximately 30-minute 10,000m race.

While sweat helps the body cool down by evaporating on the skin, on humid days when the air is already carrying a lot of moisture, bodies lose much of the cooling effect of evaporation, so the effect on the athletes in these conditions is exacerbated. At the same time, dehydration accelerates the rise in whole-body temperature, further exaggerating the impact.

The simulated conditions include wind speed and humidity, the heat generated by athletes over 30 mins (approximate duration of the race), and the airflow generated by the running motion. The athlete’s body comfort is analysed using the JOS-2 Joint System Thermoregulation Model (JOS model) developed by a research group at Waseda University, Japan.

The model calculates the temperature of an athlete’s skin, the core temperature and the degree of perspiration. The body model is divided into 17 areas and overlays a separate model that simulates the circulatory system accounting for age, gender and body size.

The JOS model can consider body size, gender and age of humans in calculations. By combining the thermoregulation model and CFD (computational fluid dynamics) the effects of changes in the surrounding environment on core temperatures and the skin throughout the body can be analysed.

“There’s been much discussion about the decision to hold the Games in the Tokyo summer. These simulations show the extreme conditions that athletes will be competing under,” said Keith Hanna, VP Marketing for Design & Engineering, Hexagon’s Manufacturing Intelligence division. “Athletes are accustomed to pushing themselves to the limits and these simulations show how racing conditions impact performance as well as the risks undertaken when the human body is pushed to extremes. What’s most interesting is the small margins of change – a couple of degrees shift in temperature can have a huge impact, so it’s only a matter of time to see whether we edge over that 39 ºC core temperature ‘tipping point’.”

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