commit 5951464686ab69926cfb9d4905f42ea898d38789
parent f2a496feac2b8cbb587385d9a4068a508a4f832e
Author: Anders Damsgaard <andersd@riseup.net>
Date: Wed, 15 Nov 2017 16:02:34 -0500
wall normal must be positive, add wall temporal integration, add more tests
Diffstat:
6 files changed, 364 insertions(+), 26 deletions(-)
diff --git a/examples/shear.jl b/examples/shear.jl
@@ -16,7 +16,6 @@ const nx = 10
const ny = 50
const r_min = 0.2
const r_max = 1.0
-const z_thickness =
Granular.regularPacking!(sim, [nx, ny], r_min, r_max)
# Create a grid for contact searching spanning the extent of the grains
diff --git a/src/datatypes.jl b/src/datatypes.jl
@@ -77,8 +77,10 @@ mutable struct WallLinearFrictionless
bc::String # Boundary condition
mass::Float64 # Mass, used when bc != "fixed"
thickness::Float64 # Wall thickness
+ surface_area::Float64 # Wall surface area
normal_stress::Float64 # Normal stress when bc == "normal stress"
vel::Float64 # Velocity (constant when bc == "normal stress")
+ acc::Float64 # Acceleration (zero when bc == "velocity")
force::Float64 # Sum of normal forces on wall
end
diff --git a/src/interaction.jl b/src/interaction.jl
@@ -57,11 +57,6 @@ function interactWalls!(sim::Simulation)
δ_n = abs(dot(sim.walls[iw].normal, sim.grains[i].lin_pos) -
sim.walls[iw].pos) - sim.grains[i].contact_radius
- #println(dot(sim.walls[iw].normal, sim.grains[i].lin_pos))
- #println(sim.walls[iw].pos)
- #println(sim.grains[i].contact_radius)
- #println(δ_n)
-
if δ_n < 0.
if sim.grains[i].youngs_modulus > 0.
k_n = sim.grains[i].youngs_modulus * sim.grains[i].thickness
@@ -69,8 +64,8 @@ function interactWalls!(sim::Simulation)
k_n = sim.grains[i].contact_stiffness_normal
end
- sim.walls[iw].force += -k_n * δ_n
sim.grains[i].force += k_n * abs(δ_n) * sim.walls[iw].normal
+ sim.walls[iw].force += k_n * δ_n
end
end
end
diff --git a/src/temporal_integration.jl b/src/temporal_integration.jl
@@ -46,7 +46,7 @@ end
export updateGrainKinematicsTwoTermTaylor!
"""
Use a two-term Taylor expansion for integrating the kinematic degrees of freedom
-for an `grain`.
+for a `grain`.
"""
function updateGrainKinematicsTwoTermTaylor!(grain::GrainCylindrical,
simulation::Simulation)
@@ -80,7 +80,7 @@ end
export updateGrainKinematicsThreeTermTaylor!
"""
Use a three-term Taylor expansion for integrating the kinematic degrees of
-freedom for an `grain`.
+freedom for a `grain`.
"""
function updateGrainKinematicsThreeTermTaylor!(grain::GrainCylindrical,
simulation::Simulation)
@@ -122,3 +122,119 @@ function updateGrainKinematicsThreeTermTaylor!(grain::GrainCylindrical,
0.5 * d_ang_acc_dt * simulation.time_step^2.
nothing
end
+
+export updateWallKinematics!
+"""
+ updateWallKinematics!(simulation::Simulation[,
+ method::String = "Three-term Taylor"])
+
+Update the wall kinematic parameters using a temporal integration scheme,
+the current force and torque balance, and gravitational acceleration. If the
+simulation contains a grid with periodic boundaries, affected wall positions
+are adjusted accordingly.
+
+# Arguments
+* `simulation::Simulation`: update the wall positions in this object
+ according to temporal integration of length `simulation.time_step`.
+* `method::String = "Three-term Taylor"`: the integration method to use.
+ Available methods are "Two-term Taylor" and "Three-term Taylor". The
+ three-term Taylor expansion is slightly more computationally expensive than
+ the two-term Taylor expansion, but offers an order-of-magnitude increase in
+ precision of wall positions. The two-term expansion can obtain similar
+ precision if the time step is 1/10 the length.
+"""
+function updateWallKinematics!(simulation::Simulation;
+ method::String = "Three-term Taylor")
+
+ if method == "Two-term Taylor"
+ for wall in simulation.walls
+ if wall.bc == "fixed"
+ continue
+ end
+ updateWallKinematicsTwoTermTaylor!(wall, simulation)
+ end
+ elseif method == "Three-term Taylor"
+ for wall in simulation.walls
+ if wall.bc == "fixed"
+ continue
+ end
+ updateWallKinematicsThreeTermTaylor!(wall, simulation)
+ end
+ else
+ error("Unknown integration method '$method'")
+ end
+ nothing
+end
+
+export updateWallKinematicsTwoTermTaylor!
+"""
+ updateWallKinematicsTwoTermTaylor!(wall, simulation)
+
+Use a two-term Taylor expansion for integrating the kinematic degrees of freedom
+for a `wall`.
+"""
+function updateWallKinematicsTwoTermTaylor!(wall::WallLinearFrictionless,
+ simulation::Simulation)
+ if wall.bc == "fixed"
+ return nothing
+ end
+
+ if wall.bc == "velocity"
+ wall.acc = 0.0
+ else
+ # Normal force directed along normal
+ f_n::Float64 = -wall.normal_stress*wall.surface_area
+ wall.acc = (wall.force + f_n)/wall.mass
+ end
+
+ wall.pos +=
+ wall.vel * simulation.time_step +
+ 0.5*wall.acc * simulation.time_step^2.0
+
+ wall.vel += wall.acc * simulation.time_step
+ nothing
+end
+
+
+export updateWallKinematicsThreeTermTaylor!
+"""
+ updateWallKinematicsThreeTermTaylor!(wall, simulation)
+
+Use a two-term Taylor expansion for integrating the kinematic degrees of freedom
+for a `wall`.
+"""
+function updateWallKinematicsThreeTermTaylor!(wall::WallLinearFrictionless,
+ simulation::Simulation)
+ if simulation.time_iteration == 0
+ acc_0 = 0.
+ else
+ acc_0 = wall.acc
+ end
+
+ if wall.bc == "fixed"
+ return nothing
+ end
+
+ # Normal load = normal stress times wall surface area, directed along normal
+
+ if wall.bc == "velocity"
+ wall.acc = 0.0
+ else
+ f_n::Float64 = -wall.normal_stress*wall.surface_area
+ wall.acc = (wall.force + f_n)/wall.mass
+ end
+
+ # Temporal gradient in acceleration using backwards differences
+ d_acc_dt = (wall.acc - acc_0)/simulation.time_step
+
+ wall.pos +=
+ wall.vel * simulation.time_step +
+ 0.5*wall.acc * simulation.time_step^2.0 +
+ 1.0/6.0 * d_acc_dt * simulation.time_step^3.0
+
+ wall.vel += wall.acc * simulation.time_step +
+ 0.5 * d_acc_dt * simulation.time_step^2.0
+
+ nothing
+end
+
diff --git a/src/wall.jl b/src/wall.jl
@@ -3,7 +3,7 @@
export addWallLinearFrictionless!
"""
function addWallLinear!(simulation, normal, pos[, bc, mass, thickness,
- normal_stress, vel, force, verbose])
+ normal_stress, vel, acc, force, verbose])
Creates and adds a linear (flat) and frictionless dynamic wall to a grain to a
simulation. Most of the arguments are optional, and come with default values.
@@ -58,7 +58,7 @@ To create a wall parallel to the *y* axis pushing downwards with a constant
normal stress of 100 kPa, starting at a position of y = 3.5 m:
```julia
-Granular.addWallLinearFrictionless!(sim, [0., -1.], 3.5,
+Granular.addWallLinearFrictionless!(sim, [0., 1.], 3.5,
bc="normal stress",
normal_stress=100e3)
```
@@ -69,8 +69,10 @@ function addWallLinearFrictionless!(simulation::Simulation,
bc::String = "fixed",
mass::Float64 = NaN,
thickness::Float64 = NaN,
+ surface_area::Float64 = NaN,
normal_stress::Float64 = 0.,
vel::Float64 = 0.,
+ acc::Float64 = 0.,
force::Float64 = 0.,
verbose::Bool=true)
@@ -80,12 +82,15 @@ function addWallLinearFrictionless!(simulation::Simulation,
"$normal)")
end
- if !(normal ≈ [1., 0.]) && !(normal ≈ [0., 1.]) &&
- !(normal ≈ [-1., 0.]) && !(normal ≈ [0., -1.])
+ if bc != "fixed" && bc != "velocity" && bc != "normal stress"
+ error("Wall BC must be 'fixed', 'velocity', or 'normal stress'.")
+ end
+
+ if !(normal ≈ [1., 0.]) && !(normal ≈ [0., 1.])
error("Currently only walls with normals orthogonal to the " *
"coordinate system are allowed, i.e. normals parallel to the " *
"x or y axes. Accepted values for `normal` " *
- "are [±1., 0.] and [0., ±1.]. The passed normal was $normal")
+ "are [1., 0.] and [0., 1.]. The passed normal was $normal")
end
# if not set, set wall mass to equal the mass of all grains.
@@ -120,14 +125,24 @@ function addWallLinearFrictionless!(simulation::Simulation,
end
end
+ # if not set, set wall surface area from the ocean grid
+ if isnan(surface_area) && bc != "fixed"
+ if typeof(simulation.ocean.input_file) == Bool
+ error("simulation.ocean must be set beforehand")
+ end
+ surface_area = getWallSurfaceArea(simulation, normal, thickness)
+ end
+
# Create wall object
wall = WallLinearFrictionless(normal,
pos,
bc,
mass,
thickness,
+ surface_area,
normal_stress,
vel,
+ acc,
force)
# Add to simulation object
@@ -158,6 +173,18 @@ function getWallSurfaceArea(sim::Simulation, wall_index::Integer)
end
nothing
end
+function getWallSurfaceArea(sim::Simulation, normal::Vector{Float64},
+ thickness::Float64)
+
+ if normal ≈ [1., 0.]
+ return (sim.ocean.yq[end,end] - sim.ocean.yq[1,1]) * thickness
+ elseif normal ≈ [0., 1.]
+ return (sim.ocean.xq[end,end] - sim.ocean.xq[1,1]) * thickness
+ else
+ error("Wall normal not understood")
+ end
+ nothing
+end
export getWallNormalStress
"""
diff --git a/test/wall.jl b/test/wall.jl
@@ -4,6 +4,7 @@
info("#### $(basename(@__FILE__)) ####")
+info("# Test wall initialization")
info("Testing argument value checks")
sim = Granular.createSimulation()
Granular.addGrainCylindrical!(sim, [ 0., 0.], 10., 2., verbose=false)
@@ -16,6 +17,9 @@ Granular.addGrainCylindrical!(sim, [ 0., 0.], 10., 2., verbose=false)
@test_throws ErrorException Granular.addWallLinearFrictionless!(sim,
[.1, .1, .1],
1.)
+@test_throws ErrorException Granular.addWallLinearFrictionless!(sim,
+ [0., 1.], 1.,
+ bc="asdf")
sim = Granular.createSimulation()
@test_throws ErrorException Granular.addWallLinearFrictionless!(sim, [1., 0.],
1.)
@@ -46,64 +50,259 @@ Granular.addWallLinearFrictionless!(sim, [0., 1.], 1., verbose=false)
@test Granular.getWallSurfaceArea(sim, 1) ≈ 20.0*2.0
@test Granular.getWallSurfaceArea(sim, 2) ≈ 10.0*2.0
-info("Test wall-grain interaction")
+info("# Test wall-grain interaction")
-info("...wall present but no contact")
+info("Wall present but no contact")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
@test sim.walls[1].force ≈ 0.
@test sim.grains[1].force[1] ≈ 0.
@test sim.grains[1].force[2] ≈ 0.
-info("...wall present but no contact")
+info("Wall present but no contact")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
-Granular.addWallLinearFrictionless!(sim, [-1., 0.], +2.01, verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], +2.01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
@test sim.walls[1].force ≈ 0.
@test sim.grains[1].force[1] ≈ 0.
@test sim.grains[1].force[2] ≈ 0.
-info("...wall at -x")
+info("Wall at -x")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
Granular.addWallLinearFrictionless!(sim, [1., 0.], -1. + .01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
@test sim.walls[1].force > 0.
-@test sim.grains[1].force[1] > 0.
+@test sim.grains[1].force[1] < 0.
@test sim.grains[1].force[2] ≈ 0.
-info("...wall at +x")
+info("Wall at +x")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
-Granular.addWallLinearFrictionless!(sim, [-1., 0.], +1. - .01, verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], +1. - .01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
@test sim.walls[1].force > 0.
@test sim.grains[1].force[1] < 0.
@test sim.grains[1].force[2] ≈ 0.
-info("...wall at -y")
+info("Wall at -y")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
Granular.addWallLinearFrictionless!(sim, [0., 1.], -1. + .01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
-@test sim.walls[1].force > 0.
+@test sim.walls[1].force < 0.
@test sim.grains[1].force[1] ≈ 0.
@test sim.grains[1].force[2] > 0.
-info("...wall at +y")
+info("Wall at +y")
sim = Granular.createSimulation()
sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
-Granular.addWallLinearFrictionless!(sim, [0., -1.], +1. - .01, verbose=false)
+Granular.addWallLinearFrictionless!(sim, [0., 1.], +1. - .01, verbose=false)
+Granular.setTimeStep!(sim)
Granular.interactWalls!(sim)
@test sim.walls[1].force > 0.
@test sim.grains[1].force[1] ≈ 0.
@test sim.grains[1].force[2] < 0.
+
+
+info("# Testing wall dynamics")
+
+info("Wall present, no contact, fixed (default)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01, verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim)
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 0.
+@test sim.walls[1].pos ≈ -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, no contact, fixed (TY2)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01, verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim, method="Two-term Taylor")
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 0.
+@test sim.walls[1].pos ≈ -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, no contact, fixed (TY3)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01, verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+@test_throws ErrorException Granular.updateWallKinematics!(sim, method="asdf")
+Granular.updateWallKinematics!(sim, method="Three-term Taylor")
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 0.
+@test sim.walls[1].pos ≈ -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, contact, fixed")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01, verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim)
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 0.
+@test sim.walls[1].pos ≈ -1.01
+
+info("Wall present, no contact, velocity BC")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01,
+ bc="velocity", vel=1.0,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim)
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 1.
+@test sim.walls[1].pos > -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, no contact, velocity BC (TY2)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01,
+ bc="velocity", vel=1.0,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim, method="Two-term Taylor")
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 1.
+@test sim.walls[1].pos > -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, no contact, velocity BC (TY3)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -1.01,
+ bc="velocity", vel=1.0,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+@test_throws ErrorException Granular.updateWallKinematics!(sim, method="asdf")
+Granular.updateWallKinematics!(sim, method="Three-term Taylor")
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 1.
+@test sim.walls[1].pos > -1.01
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, contact, velocity BC (TY2)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -0.9,
+ bc="velocity", vel=1.0,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim, method="Two-term Taylor")
+@test sim.walls[1].bc == "velocity"
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 1.
+@test sim.walls[1].pos > -0.9
+
+info("Wall present, contact, velocity BC (TY2)")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [10., 20., 1.0])
+Granular.addGrainCylindrical!(sim, [ 0., 0.], 1., 2., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], -0.9,
+ bc="velocity", vel=1.0,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim, method="Two-term Taylor")
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 1.
+@test sim.walls[1].pos > -0.9
+
+info("Wall present, contact, normal stress BC")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [2., 2., 1.])
+Granular.addGrainCylindrical!(sim, [ 1., 1.], 1., 1., verbose=false)
+Granular.addWallLinearFrictionless!(sim, [1., 0.], 2.,
+ bc="normal stress",
+ normal_stress=0.,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim)
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc ≈ 0.
+@test sim.walls[1].vel ≈ 0.
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+
+info("Wall present, contact, normal stress BC")
+sim = Granular.createSimulation()
+sim.ocean = Granular.createRegularOceanGrid([1, 1, 1], [2., 2., 1.])
+Granular.addGrainCylindrical!(sim, [ 1., 1.], 1., 1., verbose=false)
+sim.grains[1].fixed = true
+Granular.addWallLinearFrictionless!(sim, [1., 0.], 2.,
+ bc="normal stress",
+ normal_stress=1e4,
+ verbose=false)
+Granular.setTimeStep!(sim)
+Granular.interactWalls!(sim)
+Granular.updateWallKinematics!(sim)
+@test sim.walls[1].force ≈ 0.
+@test sim.walls[1].acc < 0.
+@test sim.walls[1].vel < 0.
+@test sim.grains[1].force[1] ≈ 0.
+@test sim.grains[1].force[2] ≈ 0.
+for i=1:5
+ Granular.interactWalls!(sim)
+ Granular.updateWallKinematics!(sim)
+ println(sim.walls[1].pos)
+end
+@test sim.walls[1].force < 0.
+@test sim.walls[1].acc < 0.
+@test sim.walls[1].vel < 0.
+@test sim.walls[1].pos < 1.
+@test sim.grains[1].force[1] > 0.
+@test sim.grains[1].force[2] ≈ 0.
+
