飽和水蒸気圧と飽和水蒸気量の計算、乾湿差から相対湿度の計算、不快指数の計算

hum.rb

# 飽和水蒸気圧 SWVP: saturation water vapor pressure
module Swvp
end

# 飽和水蒸気圧 Tetensの式
class TetensSwvp
  include Swvp

  def calc(temp)
    6.11 * 10 ** ((7.5 * temp) / (237.3 + temp))
  end
end

# 飽和水蒸気圧 Wagnerの式
class WagnerSwvp
  include Swvp

  Pc = 221200 # hPa：臨界圧
  Tc = 647.3  # K：臨界温度
  A = -7.76451
  B = 1.45838
  C = -2.7758
  D = -1.2303

  def calc(temp)
    x = 1 - (temp + 273.15) / Tc
    Pc * Math.exp((A * x + B * x**1.5 + C * x**3 + D * x**6) / (1 - x))
  end
end

# 飽和水蒸気圧 Sonntagの式
class SonntagSwvp
  include Swvp

  A = -6096.9385
  B = 21.2409642
  C = 2.711193 * 10**-2
  D = 1.673852 * 10**-5
  E = 2.433502

  def calc(temp)
    (Math.exp(A * ((temp + 273.15)**-1) + B - C * (temp + 273.15) + D * ((temp + 273.15)**2) + E * Math.log(temp + 273.15))) / 100
  end
end

# 飽和水蒸気量 SWVA: saturation water vapor amount
class Swva
  attr_reader :swvp

  def initialize(swvp=WagnerSwvp.new)
    @swvp = swvp
  end

  def calc(temp)
    217.0 * swvp.calc(temp) / (temp + 273.15)
  end
end

# 乾湿差
class Psychrometry
  attr_reader :swvp
  attr_reader :pressure
  attr_reader :k

  def initialize(swvp=WagnerSwvp.new, pressure: 1013, k: 0.000662)
    @swvp = swvp
    @pressure = pressure
    @k = k
  end

  # 乾湿差から相対湿度へ変換
  def calc(t_wet, t_dry)
    p_wet = swvp.calc(t_wet)
    p_dry = swvp.calc(t_dry)

    p_w = p_wet - pressure * k * (t_dry - t_wet)
    rh = p_w / p_dry

    rh
  end
end

# 不快指数
class DiscomfortIndex
  attr_reader :wet
  attr_reader :dry
  attr_reader :psychrometry

  def initialize(wet, dry, psychrometry=Psychrometry.new)
    @wet = wet
    @dry = dry
    @psychrometry = psychrometry
  end

  def from_dw
    0.72 * (dry + wet) + 40.6
  end

  def from_rh
    rh = psychrometry.calc(wet, dry)
    0.81 * dry + 0.01 * (rh * 100) * (0.99 * dry - 14.3) + 46.3
  end
end


# 飽和水蒸気圧
temp = 30
puts "飽和水蒸気圧"
puts "Tetensの式:  #{TetensSwvp.new.calc(temp)} hPa"
puts "Wagnerの式:  #{WagnerSwvp.new.calc(temp)} hPa"
puts "Sonntagの式: #{SonntagSwvp.new.calc(temp)} hPa"
puts

# 飽和水蒸気量
puts "飽和水蒸気量: #{Swva.new.calc(temp)} g/m^3"
puts

# 乾湿差から相対湿度
dry = 30.0
wet = 25.0

pressures = {
  "平穏な地上": 1013,
  "猛烈な台風": 900,
  "富士山山頂": 630,
}

pressures.each {|label, hpa|
  humidity = Psychrometry.new(pressure: hpa).calc(wet, dry) * 100
  puts "相対湿度 #{label}: #{humidity} %rh"
}
puts

# 不快指数
di = DiscomfortIndex.new(wet, dry)
puts "DI (from DW): #{di.from_dw}"
puts "DI (from RH): #{di.from_rh}"


__END__

飽和水蒸気圧
Tetensの式:  42.441629713216905 hPa
Wagnerの式:  42.49122382333086 hPa
Sonntagの式: 42.46638883838413 hPa

飽和水蒸気量: 30.415951079210945 g/m^3

相対湿度 平穏な地上: 66.75729341239447 %rh
相対湿度 猛烈な台風: 67.63754577122305 %rh
相対湿度 富士山山頂: 69.7408036197515 %rh

DI (from DW): 80.2
DI (from RH): 80.88062318550874