Fig 1.
The arrangement of measurement location and surrounding trees (a), and the percentage of occurrences of wind speed and direction during the measurement period for Tree 1 (b), Tree 2 (c), and Tree 3 (d).
Fig 2.
Diagrams of the arrangement of strain gauges and the experimental apparatus.
Schema of the arrangement of strain gauges (a), fixing of sample tree (Tree 2) to load cell and arrangement of sensors (b) are shown.
Table 1.
Sample trees.
Fig 3.
Photographs of the sample trees.
Tree 1 (a) and Tree 3 (b) are shown. Tree 2 was shown in Fig 2b.
Table 2.
Meteorological conditions on the day used for analysis.
Data from the four days with the strongest wind speed during the measurement period were analysed. The measurements were taken at a height of 3m above the ground.
Fig 4.
Time course of the values at 10-Hz measurement.
The data were given for one minute from Tree 2, including the time at which the maximum wind speed was recorded. The time course of the wind speed (a) and the direction (b) are shown in blue lines. The red and black lines indicate the measured and reference values for graphs (c), (d), (e).
Fig 5.
The measured values against the reference values at 10-Hz measurement.
The measured and the reference values were obtained at 10 Hz for the wind load ((a), (d), (g)), the centroid of the distributed wind load ((b), (e), (h)), and the direction of the wind load ((c), (f), (i)) for each sample tree. Dashed line denotes 1:1 line. The dot and the error bars in (b), (e) and (h) denote mean value and the standard deviation.
Table 3.
Results related to the accuracy.
Fig 6.
Comparison of 10-Hz measurement values for wind speed.
The course of the class mean LW, Lw_ref ((a), (c), (e)) and CL, CL_ref ((b), (d), (f)) are shown for each sample tree. These were obtained by averaging 10 Hz measurement values for wind speed classes. Error bars denote the standard error. Wind loads were regressed on a power function above 3 m/s with an intercept of zero as the analysis was carried out in LW, Lw _ref > 1.0 N. Red circles and lines indicate the measured values. Black circles and lines indicate the reference values.
Fig 7.
Influences of wind speed on the accuracy of LW,CL, and DL.
The class mean values were obtained from the values measured at 10 Hz for all sample trees. Since the MAPE of DL cannot be defined, only the MAED is shown for DL. Error bars denoted the standard error. The R2 in the linear regression and the p value for the test on the regression coefficients are shown in the graphs. The significance of the regression coefficients was tested using a t-test.
Fig 8.
Influences of wind turbulence on the accuracy of LW,CL, and DL.
The class mean MAPEL, MAPEC and MAED for the turbulent intensity of the wind speed ((a)-(c)), and the standard deviation of the wind direction ((d)-(f)) were shown. The values were obtained from all the sample trees with averaging 3 seconds readings. Error bars denoted the standard error. The R2 in the linear regression and the p value for the test on the regression coefficients of MAPEL, MAPEC, and MAED are shown in the graphs. The significance of the regression coefficients was tested using a t-test.
Fig 9.
Influences of wind speed on the drag coefficient.
The class mean drag coefficient for the wind speed was shown. The values were obtained by averaging 3 seconds readings. Error bars denote the standard error. Red circles and curves indicate the measured values. Black circles and curves indicate the reference values. The regression curve equation is Cd = 0.36 + 4.14U-2.77 and Cd_ref = 0.36 + 4.21U-2.80.
Fig 10.
Influences of drag coefficient on the accuracy of LW, CL, and DL.
The class mean values were obtained by averaging 3-second readings. Since the MAPE of DL cannot be defined, only the MAED is shown for DL. Error bars denote the standard error. The R2 in the linear regression and the p value for the test on the regression coefficients are shown in the graphs. The significance of the regression coefficients was tested using a t-test.