Sinisa Knezevic

Dear, in my test case for for one wind farm in "Windfarm overview -> Flow conditions" I see that all WTGs have a problem regarding Iextreme,amb. But in the "Reports for selected site -> Eff. turb. table" in the defined wind speed range, all the Iex,site values are below ETM values. I assume Iextreme,amb is the same as Iex,site. Is this perhaps an issue that has not been updated after final release of 61400 Ed.4? Thank you very much and kind regards, Sinisa Knezevic

Dear, 1) How do you calculate the +/- range around the extrapolated wind speed? I assume it's a sort of measure of uncertainty of the result. 2) Is that range in any way connected to coefficient of variation of the annual maximum wind speed defined in IEC 61400-1 Ed.4 section 11.3.2 Wind condition parameters (Footnote 31) Thank you and kind regards Sinisa Knezevic

Dear, Sorry I wasn't explicit enough... I was actually asking about anemometer classes according to IEC 61400-12-1 Ed.2 (Annex I, Table I.1) in which anemometer class depends on turbulence structure. Thank you once more! Regards, Sinisa

Dear, I am interested in clearing out this issue of turbulence structure. First, I presume it is the ratio of turbulences from all directions (in m/s). Correct me if I'm wrong. Second - is there a way to calculate it in WEng 3.1? Thank you! Regards, Sinisa

Dear, How does WEng 3.1 calculate slope of terrain and flow inclination in preparation of input file for WAT 3? What is the radius of terrain for slope calculation in WEng? Based on my experience flow inclination is expected to be lower than terrain slope as the terrain influence reduces with height, but this is not the case here. Can calculated terrain slope (from WEng) be compared to slopes calculated for evaluating terrain complexity? Could you please give me some explanation on this issue. Thank you very much and kind regards, Sinisa Knezevic

In the process of looking for all the details from selecting instruments to completing EYA, I I could not find the answer to "Why TEN-MINUTE averages". Some hints were: 1 (WIND TURBINES – Part 12-2: Power performance of electricity producing wind turbines based on nacelle anemometry) "It is important to note that the choice to use 10-minute statistics in itself influences the result of the power performance test, for instance through the effect of turbulence. Originally, the 10-minute period was selected AMONGST OTHERS to allow for the time the wind needs to flow from mast to turbine and to ensure reasonable correlation between wind speed and power..."? 2 Something to do with 1/(10-minute) frequency having low energy amplitude in Van den Hoven spectral gap? 3 Just a heritage from meteorology in the old times (when there was not enough memory to store data in higher resolution) that became a standard? Is there any credible scientific or practical reason? Thank you!

Hi, Thank you very much for the answer. If you manage to find any reference for the calculation of all-sector U50, that would be great. As for the third question, the wind type refers to types of winds we have in Croatia, for example Bora wind (strongest winds are almost always Bora) blows usually in 0° to 45° and depending on the location the range of direction may vary a bit. The other most frequent wind (Jugo) is in 140°- 190° range (cca) and so on. So the question was in the sense if it is "more correct" to divide data bins by wind types rather then strict sectors, because as I understand, the Gumbel method refers to "extreme events" and types of extreme wind events. Anyway, I've tested the Climate Analyst in a sense that I've changed the number of sectors, but I've got pretty much the same all-sector result. Thank you, Siniša

Dear, I have a few questions regarding the calculation of OEWC: 1 What is the principle in determining the number and length of periods? 2 How is the all-sector value determined? Why is it not the same as the maximum of sector 50yr extreme winds? In the help file the all-sector value is even larger then all sector values - that seems strange to me. 3 Would it be more accurate to calculate expected 50yr extreme wind based on wind types, rather then based on direction sectors? I assume that the division in sectors is the approximation of wind type analysis. Thank you, Sinisa

Dear, I am trying to analyze the extreme wind estimation in a bit more detail. In the help files from WEng2 there are expressions for α and β in which there is one . Do the angle brackets mean average Umax of all the measured extreme winds, or something else(median)? On a first look, the described method for determining α and β there is not a standard linear regression, right? Thank you, Sinisa

Thank you for your reply and pelase do inform of the test results. I don't know if it's of any influence for the test, but I am using USB dongle. Thanks again! Sinisa

Hello! I am wondering if any of you have any experience on running WAsP 8 on Windows 7 64-bit, or any other 64-bit operating systems. If so, please inform me if WAsP 8 is working OK in such cases. Thank you! Sinisa