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Tham khảo tài liệu 'wind tunnels and experimental fluid dynamics research part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 188 Wind Tunnels and Experimental Fluid Dynamics Research then the uncertainty can be estimated based on the first-order partial differentiations of ŨU _rtrr _aí _ riư rnrr_ MẸ L MB E A MB E EXE SaBk MB h LDLDg LDLDfr 30 Here Iffi lT an be denoted as a sensitivity coefficient BIPM 1993 . As an example the uncertainty of the LDA can be estimated by partial differentiation of Eqn. 13 . ffi rirap ffi__ __rt . ffi_Sn aw L EỆAMg E ZEM h 31 32 33 34 The second method is to differentiate the anemometer equation as seen in the first method. However in this case an equation with multiplication is more appropriate because all the calculation is done by relative ratios of each independent variable. u IBMP 35 The first-order partial differentiation of fih independent variable can be written as follows. ẵ 36 LU LU IP If the Eqn. 36 is divided by the Eqn. 35 then the ratio of to His calculated as follows. nsfco nop I g 37 Therefore the ratio of uncertainty of Than be represented as follows. L 4A E ffi J ffi At AA h 38 Further simplified L I 2 SũE ữ Ỵ 39 In case of the rotational anemometers the uncertainty can be estimated referring to Eqn. 24 . 40 Air Speed Measurement Standards Using Wind Tunnels 189 The third method is to use a simplified version of Monte-Carlo simulation ISO 2008b Landau Binder 2005 . An input variable is composed of a large number of data more than 1 000 000 according to the Gaussian random process. The input variables to the anemometer equation should be independent and uncorrelated to ensure a rigorous simulation for uncertainty estimation15. The mean and the standard deviation of each input variable are used to scale a Gaussian random signal. After that the output variable or the measuring quantity is estimated by calculating the equation with the input variables. An example to estimate the measurement uncertainty of the Pitot tube is given as follows. Example Estimate the standard or Type A uncertainty of
