Changes from the PR review: system file, example file and test file

Author: noahstruschka

examples/fluid/dam_break_2d_iisph.jl

@@ -1,20 +1,25 @@
 # 2D dam break simulation using implicit incompressible SPH (IISPH)
 using TrixiParticles
 
+fluid_particle_spacing = 0.015
+
 # Load setup from dam break example
 trixi_include(@__MODULE__,
               joinpath(examples_dir(), "fluid", "dam_break_2d.jl"),
               sol=nothing, ode=nothing)
 
-# Change smoothing kernel and length to get a stable simulation
 # IISPH doesn't require a large compact support like WCSPH and performs worse with a typical
-# smoothing length
-smoothing_length = 1.2 * fluid_particle_spacing
+# smoothing length used for WCSPH.
+smoothing_length = 1.0 * fluid_particle_spacing
 smoothing_kernel = SchoenbergCubicSplineKernel{2}()
+# This kernel slightly overestimates the density, so we reduce the mass slightly
+# to obtain a density slightly below the reference density.
+# Otherwise, the fluid will jump slightly at the beginning of the simulation.
+tank.fluid.mass .*= 0.995
 
-# Calculate kinematic viscosity for the viscosity model
+# Calculate kinematic viscosity for the viscosity model.
 # Only ViscosityAdami and ViscosityMorris can be used for IISPH simulations since they don't
-# need a state equation
+# require a speed of sound.
 nu = 0.02 * smoothing_length * sound_speed / 8
 viscosity = ViscosityAdami(; nu)
 

src/schemes/fluid/implicit_incompressible_sph/system.jl

@@ -11,6 +11,8 @@ System for particles of a fluid.
 The system employs implicit incompressible SPH (IISPH), iteratively solving a linear system
 for the pressure so that density remains within a specified tolerance of the rest value.
 See [Implicit Incompressible SPH](@ref iisph) for more details on the method.
+!!! note "Time Integration"
+    This system only supports time integration with `SymplecticEuler()`. No other schemes are currently supported.
 
 # Arguments
 - `initial_condition`:  [`InitialCondition`](@ref) representing the system's particles.

test/examples/examples_fluid.jl

@@ -216,6 +216,19 @@
         @test count_rhs_allocations(sol, semi) == 0
     end
 
+    @trixi_testset "fluid/dam_break_2d_iisph.jl with PressureMirroring" begin
+        @trixi_test_nowarn trixi_include(@__MODULE__,
+                                         joinpath(examples_dir(), "fluid",
+                                                  "dam_break_2d_iisph.jl"),
+                                         tspan=(0.0, 0.1),
+                                         boundary_density_calculator=PressureMirroring()) [
+            r"┌ Info: The desired tank length in y-direction .*\n",
+            r"└ New tank length in y-direction.*\n"
+        ]
+        @test sol.retcode == ReturnCode.Success
+        @test count_rhs_allocations(sol, semi) == 0
+    end
+
     @trixi_testset "fluid/dam_break_2d_gpu.jl" begin
         @trixi_test_nowarn trixi_include(@__MODULE__,
                                          joinpath(examples_dir(), "fluid",