# Update node coordinates in paraview

**URL:** <https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675>\
**Category:** Uncategorized\
**Created:** [April 26, 2021, 1:57pm UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675 "2021-04-26T13:57:20Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![TanY](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@TanY](https://fenicsproject.discourse.group/u/TanY)\
**Post date:** [April 26, 2021, 1:57pm UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/1 "2021-04-26T13:57:20Z")

</div>

Hi all. I’m trying to solve a problem of a hyperelastic material, which is subjected to a displacement load. I want to visualize the calculated displacement and show the deformation of the material by paraview. But I don’t know how to update the node coordinates to show the deformation of the material. The corresponding codes and pictures are attached below. Does anyone have experience dealing with similar issues？Thanks in advance.

import matplotlib.pyplot as plt  
from dolfin import \*  
from fenics import \*  
from ufl import indices

# Optimization options for the form compiler

parameters[“form\_compiler”][“cpp\_optimize”] = True  
parameters[“form\_compiler”][“representation”] = “uflacs”

# parameters[“form\_compiler”][“quadrature\_degree”]=4

#mesh=RectangleMesh(Point(0,0),Point(1,1),1,1,“left/right”)  
mesh=UnitSquareMesh(20,20)

# mesh = UnitSquareMesh.create(2,2, CellType.Type.quadrilateral)

#plot(mesh)

V = VectorFunctionSpace(mesh, “Lagrange”, 1)

# Mark boundary subdomians

bot = CompiledSubDomain(“near(x[1], side) && on\_boundary”, side = 0.0)  
top = CompiledSubDomain(“near(x[1], side) && on\_boundary”, side = 1.0)  
applied\_disp = Expression(“disp”, disp=0.0, degree=2)

bcl = DirichletBC(V, Constant((0,0)), bot)  
bcr = DirichletBC(V.sub(1), applied\_disp, top)  
bcs = [bcl, bcr]

# Define functions

du = TrialFunction(V) # Incremental displacement  
v = TestFunction(V) # Test function  
u = Function(V) # Displacement from previous iteration  
u\_old = Function(V)

# B = Constant((0.0, -0.5, 0.0)) # Body force per unit volume

# T = Constant((0.1, 0.0, 0.0)) # Traction force on the boundary

def safeSqrt(x):  
return sqrt(x+DOLFIN\_EPS)

# Kinematics

d = len(u)  
I = Identity(d) # Identity tensor  
F = I + grad(u) # Deformation gradient  
C = variable(F.T\*F) # Right Cauchy-Green tensor

q1=(F[0,1]-F[1,0])\*\*2  
q2=(F[0,0]+F[1,1])\*\*2  
q3=(F[0,1]+F[1,0])**2  
q4=(F[0,0]-F[1,1])2  
eig1=(safeSqrt(q1+q2)-safeSqrt(q3+q4))/2  
eig2=(safeSqrt(q1+q2)+safeSqrt(q3+q4))/2  
eig12=eig12  
eig22=eig2**2

def psign(u):  
return conditional(lt(u,1),1,u)

def nsign(u):  
return conditional(le(1,u),1,u)

# Invariants of deformation tensors

Ic = tr(C)  
J = det(F)

# Elasticity parameters

E, nu = 10.0, 0.3  
mu, lmbda = Constant(E/(2\*(1 + nu))), Constant(E/(3\*(1-2\*nu)))  
eps=1E-8

# psi=(mu/2\*(eig12+eig22-2-2_ln(eig1)-2_ln(eig2))+0.5_lmbda_(ln(J))\*\*2)\*dx

psi1=(mu/2\*(psign(eig12)+psign(eig22)-2-2_ln(psign(eig1))-2_ln(psign(eig2)))+0.5_lmbda_(ln(psign(J)))\*\*2)_dx  
psi2=(mu/2_(nsign(eig12)+nsign(eig22)-2-2_ln(nsign(eig1))-2_ln(nsign(eig2)))+0.5_lmbda_(ln(nsign(J)))\*\*2)\*dx

F=derivative(psi1,u,v)+derivative(psi2,u,v)  
J = derivative(F, u, du)

t=0  
ur=1.0  
deltaT=0.1  
tol=1e-3  
maxiteration=25  
AM\_tolerance=1E-3

conc\_f=File(“./hyperelastic2/u.pvd”)  
fname=open(‘F\_D\_curve1.txt’,‘w’)  
problem=NonlinearVariationalProblem(F,u,bcs,J=J)  
solver=NonlinearVariationalSolver(problem)

#staggered scheme  
while t\<=1.0:  
t+=deltaT  
if t\>=0.4:  
deltaT=0.05  
applied\_disp.disp=t\*ur  
iter=0  
err=1  
while err\>AM\_tolerance and iter\<maxiteration:  
iter +=1

```
    solver.solve()
    u_err=u.vector()-u_old.vector()
    err=u_err.norm('linf')
    u_old.assign(u)
    if err < tol:
        print('Iterations:', iter, ',Total time', t)
        conc_f << u

```

 ![微信截图_20210426215415](https://global.discourse-cdn.com/free1/uploads/fenicsproject1/original/2X/5/5f924fc8d4fdd38cf6e37aa2e764de0a28907551.png)

---

<div class="post-metadata">

**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\
**Post date:** [April 26, 2021, 9:06pm UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/2 "2021-04-26T21:06:46Z")

</div>

In Paraview there is a filter called `Warp by vector` that you can apply to your function.  
See for instance [Using Paraview for visualization — FEniCS-X tutorial](https://jorgensd.github.io/dolfinx-tutorial/chapter1/membrane_paraview.html)

---

<div class="post-metadata">

**Author:** ![TanY](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@TanY](https://fenicsproject.discourse.group/u/TanY)\
**Post date:** [April 27, 2021, 2:00am UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/3 "2021-04-27T02:00:02Z")

</div>

Dear dokken, thanks for your response, the problem has been addressed.

---

<div class="post-metadata">

**Author:** ![TanY](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@TanY](https://fenicsproject.discourse.group/u/TanY)\
**Post date:** [April 27, 2021, 3:15am UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/4 "2021-04-27T03:15:09Z")

</div>

Dear dokken, I have encountered another question: when I tried to solve a thermoelastic problem, I want to import the obtained temperature and displacement into the vtu file simultaneously, so that I can observe the temperature distribution and material deformation by paraview, the command “conc\_f \<\< u,T” (u denotes the displacement, T represents the obtained temperature) seems incorrect for this problem, do you have any suggestion to me?

---

<div class="post-metadata">

**Author:** ![dokken](https://yyz2.discourse-cdn.com/free1/user_avatar/fenicsproject.discourse.group/dokken/32/1560_2.png) [@dokken](https://fenicsproject.discourse.group/u/dokken)\
**Post date:** [April 27, 2021, 9:04am UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/5 "2021-04-27T09:04:47Z")

</div>

You should use `XDMFFile` for this:

```auto
from dolfin import *

mesh = UnitSquareMesh(10,10)
V = FunctionSpace(mesh, "CG", 2)
Q = FunctionSpace(mesh, "CG", 1)
u = Function(V)
p = Function(Q)
outfile = XDMFFile("output.xdmf")
t = 0
outfile.write(u, t)
outfile.write(p, t)

```

and then follow the instructions about opening the file and extracting blocks in my previous post.

---

<div class="post-metadata">

**Author:** ![TanY](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@TanY](https://fenicsproject.discourse.group/u/TanY)\
**Post date:** [April 27, 2021, 11:29am UTC](https://fenicsproject.discourse.group/t/update-node-coordinates-in-paraview/5675/6 "2021-04-27T11:29:10Z")

</div>

Thanks for your response!