Dear all,
I am new to R and to it's programming philosophy. The following function
is supposed to work on a vector, but I can't figure out how to do that
without looping through every element of it. Is there a more elegant
way?
Note: I have shortened it, so it is NOT correct from the pipe hydraulics
point of view
# Calculate wall friction factor
# reynolds: Reynolds number
# dk: relative roughness of pipe
lambda_wall <- function (reynolds, dk) {
z <- 1
result <- 0
for (Re in reynolds) {
if (Re <= 2320) {
# Laminar flow
lambda <- 64/Re
} else if (Re < 65 * dk[z]) {
# Turbulent flow
if (Re < 1e+5) {
lambda <- 0.3164 / sqrt(sqrt(Re))
} else {
lambda <- 0.309/(log10(Re/7))^2
}
} else {
# Intermediate area
lambdanew <- 1 / (2 * log10(3.71 * dk[z]))^2 # Start value
iter <- 0
repeat {
lambda <- lambdanew
lambdanew <- 1 / (2 * log10(2.51/(Re * sqrt(lambda)) + 0.27/dk[z]))^2
iter <- iter + 1
if ((abs(lambdanew - lambda) < 0.001) || (iter > 100)) break
}
lambda = lambdanew
}
result[z] <- lambda
z <- z + 1
}
result
} # lambda_wall()
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