Hi,
I ｈａｖｅ ａ ｓｉｍｐｌｅ ｑｕｅｓｔｉｏｎ ａｂｏｕｔ ｔｈｅ ｉｎｐｕｔｔｅｄ ｂｏｔｔｏｍ ｒｏｕｇｈｎｅｓｓ Ｚｏｂ ｉｎ ＊．ｉｎ ｆｉｌｅ． Ｉ ａｍ ｎｏｗ ｕｓｉｎｇ ａ ｌｏｇｒｉｔｈｍｉｃ ｐｒｏｆｉｌｅ ｔｏ ｓｉｍｕｌａｔｅ ｔｈｅ ＢＢＬ． Ｉｓ ｔｈｉｓ ｉｎｐｕｔｔｅｄ Ｚｏｂ ｔｈｅ ｏｎｅ ｕｓｅｄ ｉｎ ｔｈｅ ｌｏｇ ｌａｗ ｕｂ／ｕ＊＝１／ｋ＊ｌｎ（Ｚｂ／Ｚ０）？ Ｚ０＝Ｚｏｂ？ Ｉ am not quite sure about this. and How do we determine Zob in input file. Is Zob composed of three parts: grain roughness, sediment transport roughness and bedform roughness length?
should we calculate it first or just estimate it with experience ?
Thank you all so much!
Best Regards
Zhipeng
Determination of Bottom roughness Zob in Input file *. in
-
zangzhipeng
- Posts: 12
- Joined: Wed Dec 10, 2008 10:15 pm
- Location: The University of Western Australia
-
nganju
- Posts: 82
- Joined: Mon Aug 16, 2004 8:47 pm
- Location: U.S. Geological Survey, Woods Hole
- Contact:
Re: Determination of Bottom roughness Zob in Input file *. in
Hi-
If you are using the the logarithmic formulation, then ROMS will only use the defined ZoB to calculate ustar and bottom stress.
If you use SSW_BBL for the bottom boundary calculations, you can then use SSW_CALC_ZNOT, which will sum the roughness contributions from grain roughness (ZoN), sediment transport (ZoST), wave boundary layer (ZoWBL) and bedforms (ZoBF). . You can look in SSW_BBL to get a better idea of how these are calculated.
We just published a paper that evalauted these components of roughness in a nearshore circulation modeling case. In the code, the calculated roughness contribution of bedforms varies linearly with the parameter ar, which ranges from 0.267 to 0.923, depending on the literature source (Nielsen, Raudkivi, Grant/Madsen). We found that in our case the model performed best when we considered only the contributions of grain roughness and the wave boundary layer. But that was specific to our area and may also depend on boundary conditions. The citation and link are below if you are interested. Feel free to email me directly if you have any questions (nganju@usgs.gov).
Ganju, N.K., and Sherwood, C.R., 2010, Effect of roughness formulation on the performance of a coupled wave, hydrodynamic, and sediment transport model. Ocean Modelling, 33, 299-313.
http://ca.water.usgs.gov/mud/publicatio ... ghness.pdf
If you are using the the logarithmic formulation, then ROMS will only use the defined ZoB to calculate ustar and bottom stress.
If you use SSW_BBL for the bottom boundary calculations, you can then use SSW_CALC_ZNOT, which will sum the roughness contributions from grain roughness (ZoN), sediment transport (ZoST), wave boundary layer (ZoWBL) and bedforms (ZoBF). . You can look in SSW_BBL to get a better idea of how these are calculated.
We just published a paper that evalauted these components of roughness in a nearshore circulation modeling case. In the code, the calculated roughness contribution of bedforms varies linearly with the parameter ar, which ranges from 0.267 to 0.923, depending on the literature source (Nielsen, Raudkivi, Grant/Madsen). We found that in our case the model performed best when we considered only the contributions of grain roughness and the wave boundary layer. But that was specific to our area and may also depend on boundary conditions. The citation and link are below if you are interested. Feel free to email me directly if you have any questions (nganju@usgs.gov).
Ganju, N.K., and Sherwood, C.R., 2010, Effect of roughness formulation on the performance of a coupled wave, hydrodynamic, and sediment transport model. Ocean Modelling, 33, 299-313.
http://ca.water.usgs.gov/mud/publicatio ... ghness.pdf