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Precautions in wind firms accompanying the change of the ground surface roughness category

The ground surface roughness category is a step -by -step classification of the smooth state of the ground surface to the rough state.1。 The more obstacles such as buildings and trees on the ground surface, the lower the wind speed, so the wind pressure that acts on buildings such as windmills will also be reduced. In structural calculation of the Building Standards Law, the roughness of the ground surface is divided into four stages (Ⅰ to ⅳ) in order to consider the effects of the ground surface obstacle, and a certain correction coefficient corresponding to each division is added. , Wind pressure is calculated (see Fig. 1).

Fig. 1 Toproll image due to surface roughness classification (top)2And the average wind speed coefficient (lower left) and flat terrain turbulence intensity (lower right)3

 

The definition of its ground surface roughness category was changed in January 2022 due to the revision of the Building Standards Law (see Table 1).

Table 1 New definition of surface roughness classification4

 Regarding this change, "rationalization of standards (ground surface roughness classification) for calculating wind pressure"5The outline is summarized (see Fig. 2).

  • Unify the concept of local surface roughness categories that were different outside the city planning area
  • Regardless of the inside and outside of the city planning area, the specified administrative agency will be able to determine the areas of ground surface roughness categories I, Ⅱ, and ⅳ in the rules.

FIG. 2 Overview of revisions in the “rationalization of standards (ground surface roughness classification) for calculating wind pressure”5

In wind development, it is required to set a ground surface roughness classification as a calculation condition of airflow analysis models used in the site condition evaluation of Windfarm authentication.1。 Based on the above, for example, it is expected that the wind development area, which had been determined to be Ⅱ, will be determined to be Ⅲ, for example, according to a new definition. As of September 2022, the above -mentioned notification of construction planning and wind firm authentication has not been announced. However, if a simulation by airflow analysis model is implemented according to the previous ground surface roughness category in the Windfarm Authentication process, the result may be different from the case where it is simulated in a new ground surface roughness category. Care is required because of its gender. Specifically, it is related to the extreme price wind speed of the windmill position (50 -year reproduction, average wind speed for 10 minutes) and the method of calculating the turbulent strength in the event of a storm.

Average wind speed for 10 minutes, 50 years of reproduction period at the hub height of the windmill positionUHIs a reference wind speedV0Excluded coefficient of average wind speed due to terrainETVAnd altitude correction coefficientEPVIt is calculated by the following equation.

In addition, the main style of the turbulence strength in the event of a storm in the windmill positionIH1Is a turbulent strength on a flat terrainIPCorrection coefficient of turbulent strength due to terrainETIIt is calculated by the following equation.

here,V0According to the Building Standards Law, the degree of wind damage based on the recording of the past typhoons in the region and the same as the Minister of Land, Infrastructure, Transport and Tourism within the range of 30 m/s to 46 m/s. Average wind speed for 10 minutes for 50 years1,ETVWhenETIIs generally calculated using airflow analysis models.EPVWhenIPIs calculated according to the following equation and Table 2 according to the ground surface roughness category.

 Table 2 Parameters for determining the altitude correction coefficient of average wind speed1


If the ground surface roughness category is changed and the turbulent strength in the case of a storm is calculated, the result is a dangerous side or a dangerous side compared to before the change in the roughness category. The oral depends on the site conditions.

If you have any questions such as technical contents, please feel free to contact RTI.

 

Reference

  1. Japan Maritime Association, Wind Farm Certified and Authorized Wind Wind Power Station (NKRE-GL-WFC01, Edition: JULY 2021)
  2. Japan Society of Architecture, Building load guidelines, the same explanation (2015)
  3. Civil Engineering Society, Wind Power Generation Equipment Support Structural Design Guidelines ・ The same description [2010 version]
  4. The Ministry of Land, Infrastructure, Transport and Tourism, how to calculate the numerical values ​​of E, and part of the case that determines the numerical value of the V0 and wind coefficient (Ministry of Land, Infrastructure, Transport and Tourism announcement No. 1437), URL:https://www.mlit.go.jp/common/001381085.pdf
  5. Ministry of Land, Infrastructure, Transport and Tourism, rationalization of criteria (ground surface roughness classification) that calculates wind pressure (Ministry of Construction Notification No. 1454), URL: https://www.mlit.go.jp/jutakukentiku/build/content/H12-1454.pdf

 

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