Quadratic increasing HRR.

[Daan]

I'm trying to simulate a train fire using a specified fire curve. Part
of the curve is quadratic and I would like to define this in the
model. According to section 8.5 of the User Manual it is possible to
create a quadratic increasing HRR when TAU is set negative. When I set
up a simple model and set the TAU at -1 the HRR doesen't increase as I
aspected (it also doesn't remain constant after 10 seconds as the
manual states).

The ramp is defined as follows:
&SURF ID='BURNER', HRRPUA=100.0, PART_ID='smoke', COLOR='RED',
RAMP_Q='BURNRATE'/
&RAMP ID='BURNRATE', T=0000.0, F=0.0 /
&RAMP ID='BURNRATE', T=0010.0, F=-1.0 /

Hopefully someone can help me with this problem.

Sincerely yours,
Daan

[dr_jfloyd]

The RAMP applies to the HRRPUA not the TAU

[Antony]

Firstly, you should define the maximum fire size.
Secondly, you should have the designed fire growth rate (ultrafast,
fast, medium or slow).
Thirdly, put those parameter into calculation: Q = at^2, Q is the max.
fire size; a is the fire growth constant; t is the time at which Q is
max.

For example you want to define a fire of 2MW, fast fire.
a = 0.0469kW/t^2
Q = 2000kW
t = 206.5s
HRRPUA = 250kW/m^2

In FDS, you should write:
&SURF ID='FIRE', HRRPUA=250.0, TAU_Q=-206.5, COLOR='RED' /
&OBST XB=0,2,0,4,0,1, SURF_IDS='FIRE' /

Now you have a 2m x 4m object which top surface will burn as a t
square fire to 2MW and then keep constant.

[Antony]

The above command should be written:

&OBST XB=0,2,0,4,0,1, SURF_IDS='FIRE','INERT','INERT' /

Now you have a 2m x 4m object which top surface will burn as a t-
square fire up to 2MW and then keep constant. The side surfaces and
bottom surface will not burn.

[Daan]

Thank you very much! After all it wasn't as hard as I tought it would
be.

But probably you can help me with the next issue. after the quadratic
increasing fire it is constant for a while and than decreases lineary
to zero. Can I combine a quadratic increasing HRR with a lineary
decreasing HRR?

Daan

[Kevin]

Use RAMP_Q and do whatever you want.

> > bottom surface will not burn.- Hide quoted text -
>
> - Show quoted text -