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Decay rate in PART program.

Masaaki Sato, modified 4 Years ago.

Decay rate in PART program.

Youngling Posts: 2 Join Date: 8/8/14 Recent Posts
Hello all,

Using PART program (Delft3D ver. 4.01), I am simulating larval dispersal of reef fish.
In the model, I used some decay rates [0, 0.10, 0.20, 0.30, 0.40 (1/day)] as larval mortality to see its effect on particle (larval) retention within a study site after pelagic larval duration (8 days).
I expected the particle retention decrease with increasing decay rates, because total number of remaining particles must decrease with increasing decay rates.
However, there was no such a trend in simulation results of particle tracking.

So, I checked number of remaining particles on 1 day after release for each decay rate, but the number did not decrease with decay rates.

Following PART manual, I set decay rates at PROCESS PARAMETERS window when making an input file.
I want to know why decay rates does not affect number of particles in this setting. Any suggestions or answers would be appreciated for it.

Best regards,

Masaaki Sato
Michel Jeuken, modified 4 Years ago.

RE: Decay rate in PART program. (Answer)

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
Dear Masaaki,

The decay rate does not affect the number of particles in your system, but the mass of each individual particle. A lower mass per particle should lead to lower concentrations.

best regards,
Michel
Masaaki Sato, modified 4 Years ago.

RE: Decay rate in PART program.

Youngling Posts: 2 Join Date: 8/8/14 Recent Posts
Dear Michel,

Thank you for reply.
I understood the meaning of decay rate.

Best regards,

Masaaki
JT
Jack Teo, modified 2 Years ago.

RE: Decay rate in PART program.

Youngling Posts: 21 Join Date: 6/15/15 Recent Posts
Hi Masaaki,

I find this strange too.

I did a test on decay rate in DELFT3D-FLOW and they use first order decay rate, just like how PART defined decay rate in their manual. However, when running model with a expected decay rate of 10% per day (which is 0.105/day), my oil particles decayed almost instantly.

Can anyone help us with this? Thanks.
Michel Jeuken, modified 2 Years ago.

RE: Decay rate in PART program.

Jedi Knight Posts: 156 Join Date: 1/21/13 Recent Posts
Are you sure the oil that this is cause by the decay? It could also be that the oil is dispersed in the water column. you could inspect the <oilname>.csv file for this. Also the out-file should tell you more about why your oil disappears.