i have a simple GRP pipe anchored one side
lenght 1000mm, no fluid, no pressure

coef. of thermal expansion (x1,000,000)(mm/mm/°C)=18
(inserted in special execution parameters window)

axial_dilatation=alpha*L*delta_T

where alpha= 18E-6mm/mm/°C

ambient temperature -27°C

we have 3 temperatures to test:
T1=30°C
T2=50°C
T3=70°C

i thought the alpha would always "18":

axial_dil(T1)=alpha*1000*30=0.000018*1000*30=0.54mm
axial_dil(T2)=alpha*1000*50=0.000018*1000*50=0.9mm
axial_dil(T3)=alpha*1000*70=0.000018*1000*70=1.26mm

(or instead of temp 30,50,70 have i to use 30+27, 50+27, 70+27?)


BUT if i run the simulation i obtain an axial dilatation

axial_dil(T1)=0.872mm
axial_dil(T2)=1.178mm
axial_dil(T3)=1.484mm

infact in "special execution paramenter" if we flag the "print alphas and pipe properties" we obtain, starting the run:

alpha1=0.000872
alpha2=0.001178
alpha3=0.001484


Question1:
if thermal dilatation is "18" (really 18E-6mm/mm/°C), why the thermal coef. seem to change at various temperatures, obtaining different lenght expansion at different temperature?

Question2:the alpha1, alpha2, alpha3 are the coef. of thermal expansion at T1,T2,T3?
It seem no because if i calculate by hand:
axial_dil(T1)=0.000872*1000*30=26.16 >> 0.872 : ????

question3:
How does caesar calculate these alphas starting from "18" given in input?


The problem i want to calculate axial expansion by hand to confirm the caesar calculus. and i need to know the axial thermal expansion coeff. at varous temperatures.