# time varying thermal conductivity for transient thermal analysis

Hello,

Is there a way to define time varying quantities of thermal conductivity for a transient thermal?

I'm trying to solve a transient thermal problem, where in I knew the time variation of conductivities a priori. Basically, i was doing a multiple solve, and a each step i was using the MPDELE, and then try to redefine the material at a given time using MPDATA.

The solver triggered a warning that ' changing the material property during solution is a 'non-standard way'. Is it a correct way to define time varying quantities of a thermal- material property?

May i know if there any other standard way to define it.

Below is the script i tried to come up with

FINISH

/CLEAR,NOSTART

/PREP7

LENGTH=2e-03 ! 2*LENGTH, mm

HEIGHT=LENGTH/100 ! HEIGHT, mm

THICK=HEIGHT

esize=HEIGHT

area=HEIGHT*THICK

kxx_1 = 5.000000000E-03 ! VALUE AT initial time, t=0

cx_1 = 4.039360000E-02 ! VALUE AT initial time, t=0

t1= 358.000 ! inital temperature

mptemp,1,t1

mpdata,KXX,1,1,kxx_1

mpdata,C,1,1,cx_1

ET,1,LINK33

R,1,area ! AREA

k,1,-0.5*LENGTH

k,2, 0.0

k,3, 0.5*LENGTH

l,1,2

l,2,3

lglue,1,2

lesize,all,esize

type,1

real,1

mat,1

lmesh,all

esel,s,type,,1

nsle,r

IC,all,temp,1

allsel,all,all

d,node(-0.5*LENGTH,0,0),temp,0

d,node(0.5*LENGTH,0,0),temp,0

FINISH

/SOLU,

ANTYPE,TRANS

KBC,0

nleng=40

deltime=2

*dim,dxx_1,array,nleng,1

*dim,ccstinter_1,array,nleng,1

*do,tt,1,40

currtime=deltime*tt

curr_temp=(273+85)+2*deltime*(tt)

dxx_1(tt,1)=D0_1*exp((-ED_1)/(R*curr_temp))

ccstinter_1(tt,1)=RH*S0_1*P0_1*exp((ES_1-EVP_1)/(R*curr_temp))

mptemp,1,0

mpdele,kxx,1

mpdata,kxx,1,,dxx_1(tt,1)

mpdele,c,1

mpdata,c,1,,ccstinter_1(tt,1)

allsel,all,all

OUTRES,ALL,ALL

TIME,currtime

NSUBS,1,1,1

solve

*enddo

FINISH

## Answers

Hi @vkr535 , you are getting warning because it is not ideal way but if the results are okay, you should go with this option. There is one more way you can try using MPCHG command in solution processor for each load step.