### Glacier volume

Posted:

**17 May 2014, 11:14**Hello

I was performing a transient simulation for 1 year on an Italian glacier using Elmer. I attacched my .sif file below. Basically my simulation performes the following tasks:

I computed the initial volume of the mesh using ParaView (Data Analysis -> Integrated Variables).

The strange fact I have noticed is that the initial mesh volume of the two simulations is different of a magnitude of 5 even if I haven't change anything except the Arrhenius factor. How is that possible if the assigned values of Zs for each node are the same in both the simulations? Analysing the ElmerPost file it seems that both meshes have the same elevation of the bedrock but not for the surface. The differences between Zs of the simulations are reported below for each nodes:

I would expect that the initial volume of the meshes is the same. Someone could give me some hints?

If you need any further files, just ask me. I appreciate your helps!

I was performing a transient simulation for 1 year on an Italian glacier using Elmer. I attacched my .sif file below. Basically my simulation performes the following tasks:

- It considers a timestep of about 1 month (30/365.25) and it divides the year into 2 periods: the winter with a zero velocity (BasalWinterVelocity) on the bedrock and the summer with a fixed velocity of 50 mm/d (BasalSummerVelocity)
- It applies during the winter an accumulation forcing and during the summer an ablation flux. Both values are retrieved from DAT files (balance_winter.dat and balance_summer.dat) and interpolated over the domain using the getAccumulation function.
- The mesh is initially extruded and deformed vertically with the StructuredMeshMapper solver. The FreeSurfaceSolver computes the elevation of the free surface.

I computed the initial volume of the mesh using ParaView (Data Analysis -> Integrated Variables).

The strange fact I have noticed is that the initial mesh volume of the two simulations is different of a magnitude of 5 even if I haven't change anything except the Arrhenius factor. How is that possible if the assigned values of Zs for each node are the same in both the simulations? Analysing the ElmerPost file it seems that both meshes have the same elevation of the bedrock but not for the surface. The differences between Zs of the simulations are reported below for each nodes:

I would expect that the initial volume of the meshes is the same. Someone could give me some hints?

If you need any further files, just ask me. I appreciate your helps!

Code: Select all

```
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!! !!
!! simC !!
!! !!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
! Simulation title
$title = "simC1_a"
! Conversion rate
$yearInSec = 365.25*86400
Header
Mesh DB "." "mesh"
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Constants
Water Density = Real $ 1000.0/(yearInSec^2)
! Sliding on the bedrock - 50 mm/d - 18.26 m/y
BasalSummerVelocity = Real $ 50*1.0e-3*365.25
! No sliding
BasalWinterVelocity = Real 0.0
! winter accumulation file
WinterAccumulationFile = String balance_winter.dat
! summer accumulation file
SummerAccumulationFile = String balance_summer.dat
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Simulation
Coordinate System = "Cartesian 3D"
Simulation Type = Transient
Timestepping Method = "bdf"
BDF Order = 1
TimeStep Intervals = 12
Timestep Sizes = Real $30/365.25
Output Intervals = 1
Steady State Min Iterations = 1
Steady State Max Iterations = 100
Output File = "$title".result"
Post File = "$title".ep"
Max Output Level = 3
Extruded Mesh Levels = Integer 10
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Body 1
Equation = 1
Material = 1
Body Force = 1
Initial condition = 1
End
Body 2
Equation = 2
Body Force = 2
Material = 1
Initial Condition = 2
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Body Force 1
Flow BodyForce 1 = Real 0.0
Flow BodyForce 2 = Real 0.0
Flow Bodyforce 3 = Real $ -9.81*yearInSec^2
End
Body Force 2
Zs Accumulation = Variable Coordinate 1
Real Procedure "./utility" "getAccumulation"
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Initial Condition 1
Pressure = Real 0.00
Velocity 1 = Real 0.00
Velocity 2 = Real 0.00
Velocity 3 = Real 0.00
End
Initial Condition 2
Zs = Variable Coordinate 1
Real Procedure "./utility" "getTopSurface"
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Boundary Condition 1 ! lateral side
Target Boundaries = 1
Save Scalars = Logical True
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Boundary Condition 2 ! bedrock
Normal-Tangential Velocity = Logical True
Velocity 1 = 0.0
Velocity 2 = Real Procedure "./utility" "getBottomVelocity"
Velocity 3 = Real Procedure "./utility" "getBottomVelocity"
Bottom Surface = Variable Coordinate 1
Real Procedure "./utility" "getBedrock"
Save Scalars = Logical True
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Boundary Condition 3 ! upper surface
Body Id = 2
Save Scalars = Logical True
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Material 1
Density = Real $ 917.0/(yearInSec^2)
Viscosity Model = String "glen"
Viscosity = 1.0 ! Avoid warning output. This value will not be used.
Limit Temperature = Real -10.0
Rate Factor 1 = Real $ 3.9855e-13*yearInSec
Rate Factor 2 = Real $ 1.916e3*yearInSec
Activation Energy 1 = Real 60e3
Activation Energy 2 = Real 139e3
Glen Enhancement Factor = Real 1.0
Critical Shear Rate = Real $ 0.5e-6*yearInSec
Constant Temperature = Real 0.0
! Bed condition
Min Zs = Variable Coordinate 1
Real Procedure "./utility" "getMinTopSurface"
Max Zs = Real +1.0e10
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Solver 1
Equation = "MapCoordinate"
Procedure = "StructuredMeshMapper" "StructuredMeshMapper"
Active Coordinate = Integer 3
Mesh Velocity Variable = String "dSdt"
Mesh Update Variable = String "dS"
Mesh Velocity First Zero = Logical True
Dot Product Tolerance = Real 1.0e-6
Top Surface Variable Name = String "Zs"
End
Solver 2
Equation = Navier-Stokes
Stabilization Method = String Stabilized
Flow Model = Stokes
Exported Variable 1 = -dofs 1 "dSdt"
Exported Variable 2 = -dofs 1 "dS"
Linear System Solver = Direct
Linear System Direct Method = umfpack
Nonlinear System Max Iterations = 50
Nonlinear System Convergence Tolerance = 1.0e-5
! first 5 iterations or convergence < 1.e-2 before moving from Picard to Newton
Nonlinear System Newton After Iterations = 5
Nonlinear System Newton After Tolerance = 1.0e-02
! reset newton to false each new time step
Nonlinear System Reset Newton = Logical True
Steady State Convergence Tolerance = Real 1.0e-3
End
Solver 3
Equation = "Free Surface"
Variable = String Zs
Variable DOFs = 1
Exported Variable 1 = String "Zs Residual"
Exported Variable 1 DOFs = 1
Procedure = "FreeSurfaceSolver" "FreeSurfaceSolver"
Before Linsolve = "EliminateDirichlet" "EliminateDirichlet"
Linear System Solver = Iterative
Linear System Max Iterations = 1500
Linear System Iterative Method = BiCGStab
Linear System Preconditioning = ILU1
Linear System Convergence Tolerance = Real 1.0e-5
Linear System Abort Not Converged = True
Linear System Residual Output = 3
Nonlinear System Max Iterations = 20
Nonlinear System Convergence Tolerance = 1.0e-6
Nonlinear System Relaxation Factor = 1.0
Steady State Convergence Tolerance = 1.0e-03
Stabilization Method = Bubbles
Apply Dirichlet = Logical True
! How much the free surface is relaxed
Relaxation Factor = Real 1.0
! Is there a maximum step-size for the displacement use/or not accumulation
Use Accumulation = Logical True
! take accumulation to be given normal to surface/as vector
Normal Flux = Logical False
End
Solver 4
Exec Solver = After TimeStep
Exec Interval = 1
Equation = "result output"
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Output File Name = File "$title".vtu"
Output Format = String vtu
End
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Equation 1
Name = "Navier-Stokes"
Active Solvers(3) = 1 2 4
End
Equation 2
Active Solvers(1) = 3
Flow Solution Name = String "Flow Solution"
Convection = String Computed
End
```