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Old   September 21, 2004, 15:05
Default RESISTANCE OF SHIPS
  #1
salman
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if there is anyone, who have calculated resistance of ships through CFX, Please guide me how to do it. i have got the results of many ships, but i need precise, solutions. Furthermore, i need to know the techniques for enhancing the results.
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Old   September 22, 2004, 05:57
Default Re: RESISTANCE OF SHIPS
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James Date
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Hi

A lot of work been done in this field. Look at the references below.

http://www.iihr.uiowa.edu/gothenburg...CC/tanker.html

http://www.na.chalmers.se/hydro/hydResearch/

http://hyperteam.kriso.re.kr/cfd.htm

www.iihr.uiowa.edu/gothenburg2000/PDF/database-paper.pdf

The VLCC test case seems to have been studied well by a number of researchers. CFX has been used in a number of studies.

Regards James
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Old   September 22, 2004, 12:06
Default Re: RESISTANCE OF SHIPS
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salman
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Hello, james, thankx for ur help. i have already seen these sites, but what i am asking for is: the procedure in CFX PRE , how to give boundary conditions, how to give initialization, and how to predict the correct resistance, from CFX POST calculator. i have made many ships in cfx, and i have also, got some results, with free surface effects in them, but my results are not up to the standard.... so, i want guidance for the techinques in improving results, may be i am making some mistakes in CFX PRE 5.7 . Waiting for kind Reply.
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Old   September 23, 2004, 07:45
Default Re: RESISTANCE OF SHIPS
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James Date
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Hi Salman,

Your question is not an easy one! There are many things which need to be carefully considered in order to my reasonable predictions of ship resistance, probably two PhD's worth!

A few issues that spring to mind are (In no particular order):

1) Correct inflow and far field boundary conditions and locations. 2) Inlet turbulence level specification. 3) Correct near wall grid spacing (Y+ = 30 - 500 for k-e) or (Y+ <= 1.0 for SST / k-w). 4) Have enough points within the boundary layer (greater than 10 if possible). 5) Use hexahedral mesh if possible. 6) Conduct mesh independence studies. 7) Study the convergence of the relative resistance contributions i.e. pressure drag, viscous drag and wave drag (if free surface is modelled).

There are loads more things you need to look at but these are the standard ones i'd look at first.

Probably more important than modelling the whole ship geometry straight off is to validate the CFD code you are using. Look first at its performance in solving simple flows i.e. flat plate drag and compare with measured data. Then look at pressure drag. This will give you a handle on the limitations of the CFD code with regard to the flow physics you are wishing to model around the whole ship form.

Unless you have large computing resources I doubt if you will produce any meaning full results for flows around ship hulls including wave effects.

Regards James
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