set pm3d depth lighting primary 0.75
set object rect from sc 0,0 to sc 1,1 behind fc "#003344"
set palette rgb 8,7,27
set samples 128
set isosamples 72
unset border
unset tics
unset colorbox
unset key
set xyplane 0
set view 65,30, 1.5,1
set term pngcairo size 360,360
set out "shell002.png"
set parametric
set urange[-2*pi:4*pi]
set vrange[-pi:pi]

cot(x)=1/tan(x)
x(u,v)=D*(A*sin(b)*cos(u)+R*cos(v+phi)*cos(u+W)-R*sin(m)*sin(v+phi)*sin(u+W))*exp(u*cot(a))
y(u,v)=(-A*sin(b)*sin(u)-R*cos(v+phi)*sin(u+W)-R*sin(m)*sin(v+phi)*cos(u+W))*exp(u*cot(a))
z(u,v)=(-A*cos(b)+R*sin(v+phi)*cos(m))*exp(u*cot(a))
D=1;a=4*pi/9;b=2*pi/9;phi=11*pi/36;m=pi/18;W=pi/6;A=25;R=16

set zrange [:]
splot x(u,v), y(u,v), z(u,v) w pm3d

!display shell002.png