Moving lift assssment

[MSalisbury]

I'm considering looking into the piston effect of smoke leakage into a lift shaft. It is possible to dynamically add and remove blockages of course, and I can in theory simulate a lift moving up a shaft - my question is what happens to the gases when a blockage is added and removed - does FDS push them into neighbouring cells, or does the gas get magically removed and added to the model? Any thoughts would be greatly appreciated. Many thanks Matt.

[drjfloyd]

Magic. FDS may not be the tool for this particular problem.

[MSalisbury]

I can do it;) if the cell pushes or pulls the gas mass to its neighbours it should do it? Maybe it can go in a new feature request.

[rmcdermo]

Is this a stand along shaft or part of a bigger building simulation? If it is just a shaft, you could pull the Galilean invariance trick: move the walls and inlet velocity in a ramp that matches the lift acceleration. If you are interacting with background pressure, then we might have to help set a ramp on this value. This approach would be far more doable and more accurate than trying to hack in moving OBST.

[MSalisbury]

Hi, it would be investigating smoke flow from a fire at at lobby, to lobbies above, using a moving lift to investigate pressure and flows in/ out of the shaft and to levels above.

Since MGM Grand the standard practice of grounding lifts is now somewhat challenged by the requirement (here in the UK) for evacuation lifts which need to assist mobility impaired to get out. I'd like to investigate how problematic lift movements in a shaft may be.

[Er9y714]

Does not new BS9991 require protecting the lift lobbies from smoke? In that case, would not this concern be avoided?

MGM lift shafts/door were not fire resistant. Was not the main issue smoke penetrating through the doors/shafts to reach to the top floors rather than the piston effect?

Stack effect might also play an important role.

Lastly, modern lifts are designed with a consideration of minimizing the piston effect since pressure causes high velocities and noise in the shaft. So this piston effect might vary in different lift designs/buildings.

[MSalisbury]

Hi it's more a what if scenario. Smoke control failure....

[Er9y714]

@MSalisbury , I have not tried, only brainstorming; Could Controlled Particle Movement (user guide 15.5.3) be a solution? If lots of particles are insterted and occupy all the cells in a lift car volume, then those particles are assigned with a very large drag coefficient, may they push the air in front of it?

[mcgratta]

This could work, but we have found that the time step must be very small to maintain stability.