We received an enquiry this morning asking how it would be possible to monitor wind load/force in a tunnel.
Measuring wind force requires the measurement of several variables in addition to considerations relating to the structure to which the force is applied.
Wind Anemometer - Wind Speed (m/s)
Barometric Pressure Sensor - Relative Air Pressure (Pa)
Hygrometer - Relative Air Humidity (%)
Temperature Sensor - Relative Air Temperature (ºC)
However, without a specific structure referenced, we must assume the area to which the force is applied. We also cannot take into consideration the drag coefficient of the area.
To provide a meaningful measure of wind force we can use a 1m2 area, which then allows for a simple calculation to adjust our force measure to a larger or smaller area.
By measuring these four environmental variables it enables us to adjust the wind load/force based on the mix of dry air to water vapour, as water vapour has a lower density to that of dry air, so, the higher the humidity the lower the air density per m3.
Once we have these environmental measurements, the calculation to convert these into load/force(N) is as follows.
Firstly, we must convert our ºC to ºK. To do this we add 273.15 to our ºC temperature to calculate the ºK.
We must then calculate the partial pressure for the dry air and water vapour of the air. For this we use the temperature, humidity, and air pressure to calculate the percentage mix of dry air and water vapour, and the relative density of each of these elements. We utilise the known water saturation pressure at the specific air temperature recorded to calculate the partial pressure of the water vapour at the recorded relative air pressure.
Finally, we can now calculate the wind load/force(N) for our give area. We have developed the calculation tool below to assist with this conversion.
If the wind load/force required relates to a specific structure with a known drag coefficiency, this can also be entered.
We are currently developing a weather system that can provide all of the environmental parameters and in addition can automatically calculate the wind load/force (N). We intend to include the option to set area and coefficient options.
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TEL. 44 (0) 1604 832 196