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Discussion of wind - 3
470
Aerodynamic Roughness Length: Correlation with Roughness Elements. B. L. Sill, N. J. Cook and C. Fang
Comment by U. B. Singh 1. 2. 3. 4.
Do you think your theory will be applicable to natural ground surface which has got mixtures of soil particles. What about displacement height, which is a major factor to be considered to estimate Zo, and wind profile. Why is the correlation in natural conditions better than the correlation in artifical conditions. The factor (AJs) may not work well when you will simulating, natural ground surface or natural vegetation in wind tunnel studies.
Author's reply 1. 2. 3. 4.
No, Since we have only examined mostly vegetated surface. The data on displacement height are not as complete as those on zo; so, we limited our discussion to Zofor now. We don't know yet why is that. But, I think it has to do with the randomness in the natural environment. There are a lot of ways one can adapt AJs, or A/s. A/A w suitable for simulation. For example use mean, or mediam (50~ value) values of these parameters.
Comment by J. Wieringa Concerning your conclusion that in natural conditions roughness is proportional to height, t h a t seems to be based on an unfortunate selection of references - particularly the paper of Szeicz, Endrodi and Tajehman (1969), overrated and containing inadequate information. Part of Szeicz "information" related by way of Tanner and Pelton (1960) to estimates by Kimj and Letace, which are actually based on assumed zo - H - proportionality. Of course, if you starting a.~suming it, you'll end up concluding it.
Author's reply Your question regards some of the published data which we used in examining the dependence of the aerodynamic roughness length, z,, on tile rougilness element height, H. In particular, you indicated that tile paper by Lettau (J. Appl. Met., 1969) and Szeiez, et al (Water Res. Research, 1969) contain data which you indicate are overrated. Despite the fact that both tile above journals are of high quality, it is certainly possible that suspect data can appear in an article presenation, Since z,, is at best difficult to measure in the field (as well as in the wind tunnel), we chose not to judge tile quality of any of the roughness data that we used, but rather to gather as many values as possible and to rely on the statistical benefits which accrue. You indicated that the values for Lettau have a built-in proportionality between z, and H. These data however, show some of the widest scatter in our Figures 1 and 2. Deletion of these values only strengthens the correlationn between zo and the element height for natural surfilces, and we would gladly delete all these roughnesses.
The Turbulence Structure Behind the Multiple Rectangular Windbreaks B. Shiau.
Comment by A. Larson What is the geometry of the wind break configurations tested?
Author's reply
Aerodynamic Roughness Length: Correlation with Roughness Elements. B. L. Sill, N. J. Cook and C. Fang
Comment by U. B. Singh 1. 2. 3. 4.
Do you think your theory will be applicable to natural ground surface which has got mixtures of soil particles. What about displacement height, which is a major factor to be considered to estimate Zo, and wind profile. Why is the correlation in natural conditions better than the correlation in artifical conditions. The factor (AJs) may not work well when you will simulating, natural ground surface or natural vegetation in wind tunnel studies.
Author's reply 1. 2. 3. 4.
No, Since we have only examined mostly vegetated surface. The data on displacement height are not as complete as those on zo; so, we limited our discussion to Zofor now. We don't know yet why is that. But, I think it has to do with the randomness in the natural environment. There are a lot of ways one can adapt AJs, or A/s. A/A w suitable for simulation. For example use mean, or mediam (50~ value) values of these parameters.
Comment by J. Wieringa Concerning your conclusion that in natural conditions roughness is proportional to height, t h a t seems to be based on an unfortunate selection of references - particularly the paper of Szeicz, Endrodi and Tajehman (1969), overrated and containing inadequate information. Part of Szeicz "information" related by way of Tanner and Pelton (1960) to estimates by Kimj and Letace, which are actually based on assumed zo - H - proportionality. Of course, if you starting a.~suming it, you'll end up concluding it.
Author's reply Your question regards some of the published data which we used in examining the dependence of the aerodynamic roughness length, z,, on tile rougilness element height, H. In particular, you indicated that tile paper by Lettau (J. Appl. Met., 1969) and Szeiez, et al (Water Res. Research, 1969) contain data which you indicate are overrated. Despite the fact that both tile above journals are of high quality, it is certainly possible that suspect data can appear in an article presenation, Since z,, is at best difficult to measure in the field (as well as in the wind tunnel), we chose not to judge tile quality of any of the roughness data that we used, but rather to gather as many values as possible and to rely on the statistical benefits which accrue. You indicated that the values for Lettau have a built-in proportionality between z, and H. These data however, show some of the widest scatter in our Figures 1 and 2. Deletion of these values only strengthens the correlationn between zo and the element height for natural surfilces, and we would gladly delete all these roughnesses.
The Turbulence Structure Behind the Multiple Rectangular Windbreaks B. Shiau.
Comment by A. Larson What is the geometry of the wind break configurations tested?
Author's reply