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Surface roughness in Flow-3d

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Old   December 23, 2008, 10:28
Default Surface roughness in Flow-3d
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Marco
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Dear experts :

In open channel, roughness coefficients are typically in one of two ways: (1)Chey's resistence coefficient, or(2)Manning's n. But in flow-3d, the roughness coefficients is use k (be expressed in unit of length).

So, flow-3d's roughness and open channel's roughness is different. I want to know how did I define the surface roughness if I simulated open channel flow. Did Manning's n necessary translate to roughness K by some equation or another methods?

May someone provide the opinion for me? Thanks your help!
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Old   December 23, 2008, 13:40
Default Re: Surface roughness in Flow-3d
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Jorge D. Abad
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Marco, I will suggest to take a look into Yen's book. The roughness (rough) in F3D is a Nikuradse type of roughness (ks), then, if you have values of Manning you can use the following equation:

ks[m]= (n[m^(1/6)]/0.0389)^6

where m is meters and n[m^(1/6)] is usually the values 0.030 (riprap) found in Open channel textbooks ==> ks=0.21039.

Remember Manning n above has units of m^(1/6). Further details read Yen's book.

Good luck

Jorge D. Abad

REFERENCE: Yen, Ben Chie (1991). "Channel flow resistance: centennial of Manning's formula:. Water Resources Publications.
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Old   December 23, 2008, 22:12
Default Re: Surface roughness in Flow-3d
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Marco
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Jorge D. Abad, very thanks your help!

So, I know manning value. And I use equation [ ks[m]= (n[m^(1/6)]/0.0389)^6 ] that I can get a ks value. Then input the surface roughness (ks) of surface properties in flow-3d. Did I solve roughness problem ?

Thanks you to provide the reference for me.
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