# Surface roughness in Flow-3d

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 December 23, 2008, 10:28 Surface roughness in Flow-3d #1 Marco Guest   Posts: n/a 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!

 December 23, 2008, 13:40 Re: Surface roughness in Flow-3d #2 Jorge D. Abad Guest   Posts: n/a 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. zandi and loh561 like this.

 December 23, 2008, 22:12 Re: Surface roughness in Flow-3d #3 Marco Guest   Posts: n/a 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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