xx <- seq(0,4pi,length=512)

df <- do.call(cbind,lapply(1:32, function(i) sin((runif(1)+.5)xx)+1))

df[1,] <- 0

df[nrow(df),] <- 0

plot(x=xx, y=rep(40,length(xx)), ylim=c(0,40), type="n", ylab="")

for(i in 32:1){

  offset <- 1.1*i

  polygon(x=xx, y=offset+df[,i], col="black", border="white")