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Author Topic: SFPE Mode - Wide Exits?  (Read 4442 times)

mikeuk

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SFPE Mode - Wide Exits?
« on: February 20, 2014, 05:41:07 am »

hi,

Is it appropriate to use the SFPE mode with large numbers of agents and wide exits?

The concern is that the flow of agents entering on one side of the exit could be influenced the flow of agents on the other side of the exit without having any actual physical interaction.

Any thoughts would be much appreciated.

Thanks,

Michael
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Charlie Thornton

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Re: SFPE Mode - Wide Exits?
« Reply #1 on: February 20, 2014, 09:17:59 am »

In this case, the key parameter is Max Room Density (see attached). SFPE mode occupants will refuse to enter a room if doing so would cause it to fill beyond the maximum room density. This prevents the SFPE velocity equations from going negative and it approximates some manner of influence for downstream rooms. You can test it by creating a funnel where several rooms empty into a junction room that has less outgoing door than incoming door.

The value of max room density can have a substantial impact on egress time in crowded simulations. The default is 1.88 pers/m2 which is based on the density for maximum specific flow (see discussion for Equation 3 and Figure 8 in the SFPE Engineering Guide: Human Behavior in Fires). Increasing that value should cause simulations to slow down considerably.
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mikeuk

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Re: SFPE Mode - Wide Exits?
« Reply #2 on: February 20, 2014, 09:33:42 am »

Thanks Charlie, much appreciated.

To confirm, the SFPE mode adjusts agent speed according to the density of the room agents are in. Aside from this reduction in speed, at exits, does SFPE mode set any minimum agent delay before going through the exit according to the time the previous agent went through?

thanks again  :)
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Charlie Thornton

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Re: SFPE Mode - Wide Exits?
« Reply #3 on: February 20, 2014, 09:55:06 am »

The doors have something like a cooldown timer (or a recharge time). The first agent goes right through and then the door will refuse passage to the next until a certain amount of time passes. The length of the delay is calculated to make the door flow rate correct based on effective width. For a few more details, you may want to look at the technical reference:

http://www.thunderheadeng.com/wp-content/uploads/downloads/2013/10/tech_ref.pdf

Look for the section "Movement Through Doors".
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mikeuk

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Re: SFPE Mode - Wide Exits?
« Reply #4 on: February 20, 2014, 10:14:18 am »

Thanks Charlie. I understand.

So it is perhaps unsuitable to use the SFPE mode for wide exits as agents entering one side could delay agents entering from the other side even though they have no physical contact. In this case Steering mode would be more appropriate I guess.
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Charlie Thornton

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Re: SFPE Mode - Wide Exits?
« Reply #5 on: February 20, 2014, 11:06:06 am »

Since the SFPE calculation is a fluid-based approximation, it tends to start looking strange when you think about the agents bumping into one another. Either the wide door is what the SFPE hand calcs call a controlling component and it will limit the flow of occupants based on its flow rate or something else is the controlling component and we could replace the door with not-a-door (just an opening?) without any meaningful impact on the results.

If you prefer to have flow rates naturally emerge from collision avoidance behavior (instead of prescribed maximums), then steering mode without flow rate limits is a more suitable option.
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Charlie Thornton

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Re: SFPE Mode - Wide Exits?
« Reply #6 on: February 20, 2014, 11:22:03 am »

I just re-read your first question and I now see what you were asking. I think you are right. The flow rate limit on an exit could introduce an artificial delay, but it does release multiple agents in a time step so it may be pretty close. I think I'd like to compare a room with a big door to a hand calc and see how closely the two match.
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mikeuk

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Re: SFPE Mode - Wide Exits?
« Reply #7 on: February 21, 2014, 04:42:11 am »

Thanks a lot. Just what I needed.

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