CODEWITHSUNDEEP
fortranintel-fortranfortran95
YujiE
YujiE

Reputation: 1

Variable 'n' cannot appear in the expressions below

I want to do an iteration of the strain and stress change in rock mechanics, but am stuck on the errors:

"real::STRAIN (1:N), SIGMA (1:N),DSIGMA (1:N),STRAIN (1:N)=0.0"

and

"real,Dimension(6)::CEL(1:N,1:N)!stiffness matrix"

!program elastic_plastic

implicit none
!define all parameter
integer :: i = 1.0,j,K,M,N,inc
real::STRAIN (1:N), SIGMA (1:N),DSIGMA (1:N),DSTRAIN (1:N)=0.0
real,Dimension(6)::CEL(1:N,1:N)!stiffness matrix
real:: YOUNG, NU, COHESION !rock properties
real::ALPHA, KAPPA! cohesion and frictional angle
real::F !function
real::FRICTION_DEG, FRICTION_RAD !friction angle
real::VARJ2 ,VARI1 !stress invariants (I1 and J2)(MPa)
real:: LAMBDA,GMODU !lames constant and shear modulus
real::SIGMA_1,SIGMA_2,SIGMA_3 !principle stresses(MPa)
real::SHEAR_4,SHEAR_5,SHEAR_6 !shear stresses
real,parameter::DEG_2_RAD = 0.01745329


!INPUT
NU = 0.25
COHESION = 15 ! in MPa
YOUNG = 20 ! in GPa
FRICTION_DEG = 30.0d0
FRICTION_RAD = FRICTION_DEG *(DEG_2_RAD)

!perform calculations
KAPPA=6.*COHESION *cos(FRICTION_DEG*DEG_2_RAD)/(sqrt(3.)*(3.-sin(FRICTION_DEG*DEG_2_RAD)))
ALPHA=2.*sin(FRICTION_DEG*DEG_2_RAD)/(sqrt(3.)*(3.-sin(FRICTION_DEG*DEG_2_RAD)))
GMODU=YOUNG/2.*(1.+NU)
LAMBDA=NU*YOUNG/((1.+NU)*(1.-(2.*NU)))


!Set up elastic stiffness matrix (CEL)
CEL(1:N,1:N)=0.0
    CEL (1,1)= LAMBDA-(2.*GMODU)
    CEL (2,2)= LAMBDA-(2.*GMODU)
    CEL (3,3)= LAMBDA-(2.*GMODU)
    CEL (4,4)= 2.*GMODU
    CEL (5,5)= 2.*GMODU
    CEL (6,6)= 2.*GMODU


  DO
    inc = inc + 1
    DSTRAIN(1)=0.00002
    DSIGMA = matmul (CEL(1:N,1:N), DSTRAIN)
    SIGMA =SIGMA +DSIGMA
    STRAIN=STRAIN+DSTRAIN

     !calculate I1 AND J2
VARI1=SIGMA_1+SIGMA_2+SIGMA_3
VARJ2=1./6.*((SIGMA_1-SIGMA_2)**2+(SIGMA_2-SIGMA_3)**2+(SIGMA_3- SIGMA_1)**2+SHEAR_4**2+SHEAR_5**2+SHEAR_6**2)


!Yield function (Drucker-prager)
F= ALPHA*VARI1+(sqrt(VARJ2)-KAPPA)

IF (F.LE.0.0d0)then !Elastic step (exit)
    SIGMA =SIGMA
    STRAIN=STRAIN
    exit
    endif

    if (F.GT.0.0d0)then !Plastic step (continue)
goto 20
end if
20 continue
write(11,*)STRAIN,SIGMA,inc

END DO

end

Upvotes: 0

Views: 1813

Answers (1)

Brian O'Donnell
Brian O'Donnell

Reputation: 1876

You can't statically define an array with a variable. You must use a constant. For example the following will work:

real::STRAIN (1:5), SIGMA (1:5),DSIGMA (1:5),DSTRAIN (1:5)=0.0
real,Dimension(6)::CEL(1:5,1:5)!stiffness matrix

If you don't know the size of the arrays at code time you can use the 'allocate' statement. This is known as 'dynamic storage allocation'. From 'Arrays and Parallel programming in Fortran 90/95':

The way to declare an allocatable array is as follows:

integer Nparticles               ! number of particles
integer, parameter :: dim=3      ! dimensionality of space
...
real, allocatable :: charge(:)   ! defines an array containing the charge of 
                                 ! each particle 
integer, allocatable :: xyz(:,:) ! coordinates of each particle

Once the actual number of particles in the simulation has been read, we can allocate these arrays:

read(*,*) Nparticles
allocate (charge(Nparticles),xyz(dim,Nparticles))

Upvotes: 1

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