th thm*(2*(1-M)*Z/Hi+M) "Thickness variation"
w_appl (stretch-1)*Hi "Axial displacement"
stch1 sqrt(mbrn.Cel11) "First principal stretch"
stch2 sqrt(mbrn.Cel22) "Second principal stretch"
stch3 sqrt(mbrn.Cel33) "Third principal stretch"
WF C1*(stch1^2+stch2^2+1/(stch1^2*stch2^2)-3)+C2*(1/stch1^2+1/stch2^2+stch1^2*stch2^2-3) "Full strain energy, Mooney-Rivlin"
WR C1*(stch1^2+2/stch1-3)+C2*(1/stch1^2+2*stch1-3) "Relaxed strain energy, Mooney-Rivlin"
WT WF*step1(stch2*sqrt(stch1))+WR*(1-step1(stch2*sqrt(stch1))) "Total strain energy, Mooney-Rivlin"
P rho_w*g_const*z_w*(z_w>(Z+w)) "Fluid pressure"
iswrinkled (stch2*sqrt(stch1)<=1) "Is wrinkled (relaxed strain energy approach)"