Results lower than 50% the experimental result

dbalan · December 29, 2015, 20:05

Hi guys,

I'm currently new to Star CCM+ and my company has asked me to try the program and use an add-on Estimating Hull Performance (EHP).
Basically it just automatically sets up the ship the same as in the DFBI tutorial so i'm sure my Continua(Physics) will be right and the regions too.

I'm working with a 32m Habour Tug and it was a ship which was already built by the company. During their sea trials, the power exerted was 3200HP (rating on the engine). However, when i did my analysis, the power required which i got was only 1300HP with includes the appendages and a constant of 0.6 which is the power drop to the shaft.

Is there something wrong with my set-up or the add-on? Or is my mesh problematic (I'm using a 5mm mesh which converges)?

efe011 · January 7, 2016, 12:24

It might be difficult to say, from the details you've given in your post, if your setup is right or not.

However, from my experience I can say that often ships like tugs with low L/B ratios are hard to analyze with traditional RANS CFD. Large separation regions and large waves often mess traditional setups.

I'd encourage you to check your mesh details, specially in the wake region. Do a sensitivity analysis to mesh size (as you should do for every new analysis you make).

Also check the resistance components, and compare friction to ITTC.

Further details from your part would make it easier to give you hints on where to look.

Regards.

December 29, 2015, 20:05	Results lower than 50% the experimental result	#1
dbalan New Member Daniel Join Date: Nov 2015 Posts: 10 Rep Power: 10	Hi guys, I'm currently new to Star CCM+ and my company has asked me to try the program and use an add-on Estimating Hull Performance (EHP). Basically it just automatically sets up the ship the same as in the DFBI tutorial so i'm sure my Continua(Physics) will be right and the regions too. I'm working with a 32m Habour Tug and it was a ship which was already built by the company. During their sea trials, the power exerted was 3200HP (rating on the engine). However, when i did my analysis, the power required which i got was only 1300HP with includes the appendages and a constant of 0.6 which is the power drop to the shaft. Is there something wrong with my set-up or the add-on? Or is my mesh problematic (I'm using a 5mm mesh which converges)?

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January 7, 2016, 12:24		#2
efe011 New Member Join Date: Oct 2012 Posts: 9 Rep Power: 13	It might be difficult to say, from the details you've given in your post, if your setup is right or not. However, from my experience I can say that often ships like tugs with low L/B ratios are hard to analyze with traditional RANS CFD. Large separation regions and large waves often mess traditional setups. I'd encourage you to check your mesh details, specially in the wake region. Do a sensitivity analysis to mesh size (as you should do for every new analysis you make). Also check the resistance components, and compare friction to ITTC. Further details from your part would make it easier to give you hints on where to look. Regards.