Ramp function

[Shiv]

Hi,

I would like to know more about the Ramp function being used in the
test case spray_burner.fds. I wanted to know how the parameter F
should change according to the time T. Thank you for your guidance.

Shiv

[drjfloyd]

Have you read the User's Guide Section 8.5?

[Shiv]

Hi,

I have read it.  But I wanted to know in the spray_burner model, how would one decide at 20th second the mixture fraction should be 1? There is a possibility that the fraction can be 1 at earlier time too.  I wanted to know how to decide that.

Thank you

Shiv

[drjfloyd]

FLOW_RAMP /= Z. FLOW_RAMP is a multiplier of the FLOW_RATE.

On Jun 9, 8:00 pm, Shiv <gan71...@gmail.com> wrote:
> Hi,

> I have read it.  But I wanted to know in the spray_burner model, how would
> one decide at 20th second the mixture fraction should be 1? There is a
> possibility that the fraction can be 1 at earlier time too.  I wanted to
> know how to decide that.
> Thank you
>
> Shiv
>

[Shiv]

H

[Shiv]

Hi, 

I am sorry I couldn't understand.  What is FLOW_ramp /= Z? It will be great if you could explain it again.

Thank you

Shiv

[drjfloyd]

The RAMP does not specify the value of the mixture fraction. All time
vs parameter RAMPs are multipliers of the variable the ramp
corresponds to. So this RAMP is a FLOW_RAMP which is for the variable
FLOW_RATE which is the mass flow of liquid. Similarly, RAMP_Q on a
SURF also does not give the value of the mixture fraction, it is a
multiplier of the HRRPUA, and so on for other time vs. parameter
ramps. The only time a ramp would give the value of the mixture
fraction would be for a RAMP_MF and if and only if the the mass
fraction input the RAMP was being applied to corresponded to a mixture
fraction species.

On Jun 9, 10:21 pm, Shiv <gan71...@gmail.com> wrote:
> Hi, I am sorry I couldn't understand.  What is FLOW_ramp /= Z? It will be

> great if you could explain it again.
>
> Thank you
> Shiv
>

> On Tue, Jun 9, 2009 at 10:20 PM, Shiv <gan71...@gmail.com> wrote:
> > H
>

[Shiv]

Hi,

Thank you very much for the clear explanation.  Hence FLOW_RAMP is a fraction of the mass flow rate of the fuel.  Similarly, why was the fraction then 1.0 at 20 th second? Is there a possibility to know the time when we want the mass flow rate fraction to be 1.0?

Thank you once again.

Shiv

[drjfloyd]

It is 1 at 20 s since the person who created the input file decided to
use a RAMP that went from 0 s,no flow to 20 s, full flow. The
decision to use a RAMP or not and what values the RAMP depends on what
it is you are trying to model. If you have time dependent boundary
conditions, a RAMP allows you to input that time dependence.

On Jun 9, 11:11 pm, Shiv <gan71...@gmail.com> wrote:
> Hi,
>

> Thank you very much for the clear explanation.  Hence FLOW_RAMP is a
> fraction of the mass flow rate of the fuel.  Similarly, why was the fraction
> then 1.0 at 20 th second? Is there a possibility to know the time when we
> want the mass flow rate fraction to be 1.0?
> Thank you once again.
>
> Shiv
>

[Shiv]

Hi,

Thank you.  One final question.  If we don't mention any ramp, then does FDS assume the fraction of flow rate to be 1.0 from the start of the simulation? 

Thanks once again

Shiv

[drjfloyd]

If there is no FLOW_RAMP then the FLOW_RATE time dependence is given
by FLOW_TAU. See the User Guide discussion on TAU_Q in section 8.5.1
(FLOW_TAU behaves the same way). The default value for FLOW_TAU is 0,
which results in no time dependence (i.e. fraction of 1 for the entire
simulation)

On Jun 10, 10:32 am, Shiv <gan71...@gmail.com> wrote:
> Hi,

> Thank you.  One final question.  If we don't mention any ramp, then does FDS
> assume the fraction of flow rate to be 1.0 from the start of the
> simulation?
>
> Thanks once again
> Shiv
>