real circleradius = 160;

path circ = circle((0,0), circleradius);
fill(circ, red);

guide spiral;

real curveFunc(real theta10) {
  return 0.008*theta10*theta10 + 0.2*theta10;
}

for (int i = 0; i < 200; i += 1) {
  spiral = (curveFunc(i)*dir(10*i))..spiral..(curveFunc(i)*dir(180+10*i));
}

path p = buildcycle(spiral, circ);
fill(p, black);