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Author Topic: SFPE mode and steering mode  (Read 4988 times)


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SFPE mode and steering mode
« on: February 25, 2009, 08:20:52 pm »

I have run an evacuation analysis for both SFPE mode and steering mode; it turns out to be the evacuation time is considerable longer for SFPE mode than that of steering mode.

Is that because occupants in SFPE mode are much easier to get into the big congestion at doors and exits (the nature of flow-based model); and in the other hand, agents in steering mode can "handle" the congestion situation in a better way (keep comfortable distance among each other)?

Charlie Thornton

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Re: SFPE mode and steering mode
« Reply #1 on: February 26, 2009, 10:12:24 am »

The two primary differences between SFPE mode and steering are:

(1) In SFPE mode, doors impose a strict flow rate limit ( 1.32 pers/s-m of effective width )
(2) In SFPE mode, as room density increases, occupant velocity decreases.

Visually, the inter-penetration allowed by by SFPE mode is another major difference, but (by itself) it doesn't seem to be a major contributer to time differences.

Usually, when I see an SFPE simulation takes much longer than a steering simulation, it's because a room/hall/stairway has become overcrowded and the occupants are moving extremely slowly.  You can actually make congested SFPE simulations give very fast results by manipulating the Maximum Room Density in the Simulation Parameters.  If you reduce that value, occupants will not overfill rooms and the average speed will remain much higher.

Doors can account for smaller - but still significant - differences in times between SFPE and Steering mode.  In steering mode, there is no hard limit on door flow rate.  If two occupants hit a door in just the right way, they can zip in to the hallway very quickly.

The actual congestion in the queue leading up to the door affects the two modes differently.  In SFPE mode, it changes how quickly occupants can approach the queue since the room density is considered in velocity, but once in the queue, occupants flow through at a fixed rate.  In steering mode crowded doors lead to a bit more time-consuming maneuvering to get through with minimal collisions with walls and occupants - though the tie-breaking algorithm that prevents arches from forming keeps things flowing even when the queue is crowded.

- Charlie