Define CONTROL for ignition

[hdd]

Hello everyone!

In FDS, the OBST could be ignited by IGNITION_TEMPERATURE in SURF. I want to try another method to ignite an OBST. I want to define the process as follows: if the temperature on at least one face of the cube reach a point, then all burning faces are set to ignite and follow the same prescribed heat release rate per unit area (HRRPUA) curve. Is that possible?

Thanks!

[carlop...@gmail.com]

yes it is possible, I am attaching a link to a discussion where Dr. Floyd was very kind in following up with me. I hope he can be of some help to you.

Good Work

https://groups.google.com/g/fds-smv/c/Wp8lq8JFvbQ/m/pgnquYm9FwAJ

[dr_jfloyd]

That thread captures the basic concept. You need a set of DEVC and CTRL to get the maximum temperature on all sides with a SETPOINT at your desired temperature and then link that to turning on VENTs with your HRRPUA.

[hdd]

Thank you all! I'm sorry to bother you again, I tried your idea but I have some problems. In case1, I use the WALL TEMPERATURE=300  as the setpoint and in case2 I use ADIABATIC SURFACE TEMPERATURE=300 as the setpoint. But In case1, the DEVC could not record the wall temperature, the temperature of the DEVC is 20 all the time. I think the WALL TEMPERATURE is better as the ignition point because the adiabatic surface temperature is not the real surface temperature of the combustibles, the ignition point will be higher when use the ADIABATIC SURFACE TEMPERATURE.

[dr_jfloyd]

18.4.2 Activating and Deactivating Vents

When a device or control function is applied to a VENT, the purpose is to either activate or deactivate any time ramp associated with the VENT via its DEVC_ID.

The 'fire' BC is always being applied to the OBST. What the DEVC controls is the RAMP for the fire size and the implied RAMP for TMP_FRONT=0 (the default TAU_T=1). With your inputs, there is no 1D heat conduction for 'fire' which is why your DEVC is not showing a temperature change. 

Remove the SURF_ID='wood' from the OBST and add it to the five VENTs. Then take the HRRPUA and RAMP_Q inputs from fire and copy them to the wood SURF.  Now the five faces with wood will heat up and when the DEVC activates the RAMP_Q will start.

[hdd]

Thanks so much, dr_jfloyd. I understand and the case worked.