From 163eb5b4436876d4163cf6aa33ce633b5b7957d0 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Wed, 23 Jul 2025 17:25:25 +0200
Subject: Adding channel

---
 examples/SConscript                 |   8 +-
 examples/poiseulle_channel_2d.cpp   | 422 ++++++++++++++++++++++++++++++++++++
 examples/poiseulle_particles_2d.cpp |  14 +-
 3 files changed, 442 insertions(+), 2 deletions(-)
 create mode 100644 examples/poiseulle_channel_2d.cpp

diff --git a/examples/SConscript b/examples/SConscript
index 9bac1f0..5ec416b 100644
--- a/examples/SConscript
+++ b/examples/SConscript
@@ -38,12 +38,18 @@ examples_objects = [];
 examples_env.add_source_files(examples_objects, ['poiseulle_2d.cpp'], shared=False);
 examples_env.poiseulle_2d = examples_env.Program('#bin/poiseulle_2d', [env.library_static, examples_objects]);
 
+# Poiseulle Channel 2D
+examples_objects = [];
+examples_env.add_source_files(examples_objects, ['poiseulle_channel_2d.cpp'], shared=False);
+examples_env.poiseulle_channel_2d = examples_env.Program('#bin/poiseulle_channel_2d', [env.library_static, examples_objects]);
+
 # Set Alias
 env.examples = [
 	examples_env.meta_2d,
 	examples_env.cavity_2d,
 #	examples_env.particle_ibm_2d
-	examples_env.poiseulle_2d
+	examples_env.poiseulle_2d,
+	examples_env.poiseulle_channel_2d
 ];
 env.Alias('examples', env.examples);
 
diff --git a/examples/poiseulle_channel_2d.cpp b/examples/poiseulle_channel_2d.cpp
new file mode 100644
index 0000000..376ba84
--- /dev/null
+++ b/examples/poiseulle_channel_2d.cpp
@@ -0,0 +1,422 @@
+#include "../c++/lbm.hpp"
+#include "../c++/collision.hpp"
+#include "../c++/boundary.hpp"
+#include "../c++/iterator.hpp"
+
+#include <forstio/codec/data.hpp>
+
+namespace kel {
+namespace lbm {
+namespace sch {
+using namespace saw::schema;
+
+/**
+ * Basic distribution function
+ * Base type
+ * D
+ * Q
+ * Scalar factor
+ * D factor
+ * Q factor
+ */
+using T = Float32;
+using D2Q5 = Descriptor<2u,5u>;
+using D2Q9 = Descriptor<2u,9u>;
+
+template<typename Desc>
+using DfCell = Cell<T, Desc, 0u, 0u, 1u>;
+
+template<typename Desc>
+using CellInfo = Cell<UInt8, D2Q9, 1u, 0u, 0u>;
+
+/**
+ * Basic type for simulation
+ */
+template<typename Desc>
+using CellStruct = Struct<
+	Member<DfCell<Desc>, "dfs">,
+	Member<DfCell<Desc>, "dfs_old">,
+	Member<CellInfo<Desc>, "info">
+>;
+
+template<typename T, uint64_t D>
+using MacroStruct = Struct<
+	Member<FixedArray<T,D>, "velocity">,
+	Member<T, "pressure">
+>;
+
+template<typename T>
+using GeometryStruct = Struct<
+	Member<T, "info">
+>;
+
+using CavityFieldD2Q9 = CellField<D2Q9, CellStruct<D2Q9>>;
+}
+
+namespace cmpt {
+template<bool East>
+struct PressureBoundaryRestrictedVelocityTo {};
+}
+
+/**
+ * This is massively hacky and expects a lot of conditions
+ * Either this or mirrored along the horizontal line works
+ *
+ * 0 - 2 - 2
+ * 0 - 3 - 1
+ * 0 - 3 - 1
+ * .........
+ * 0 - 3 - 1
+ * 0 - 2 - 2
+ *
+ */
+template<typename FP,typename Descriptor, bool East>
+struct component<FP,Descriptor, cmpt::PressureBoundaryRestrictedVelocityTo<East>> {
+private:
+	saw::data<FP> pressure_setting_;
+	saw::data<FP> rho_setting_;
+public:
+	component(const saw::data<FP>& pressure_setting__):
+		pressure_setting_{pressure_setting__},
+		rho_setting_{pressure_setting__ * df_info<FP,Descriptor>::inv_cs2}
+	{}
+
+	template<typename CellFieldSchema>
+	void apply(saw::data<CellFieldSchema>& field, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, uint64_t time_step){
+		using dfi = df_info<FP,Descriptor>;
+
+		bool is_even = ((time_step % 2) == 0);
+		auto& cell = field(index);
+
+		auto& info = cell.template get<"info">();
+		if(info({0u}).get() == 0u){
+			return;
+		}
+		auto& dfs_old = (is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
+		auto& dfs = (not is_even) ? cell.template get<"dfs_old">() : cell.template get<"dfs">();
+
+		/**
+		 * Sum all known DFs
+		 */
+		saw::data<FP> sum_df{0};
+		for(saw::data<sch::UInt64> k{0u}; k < saw::data<sch::UInt64>{Descriptor::Q}; ++k){
+			auto c_k = dfi::directions[k.get()];
+			auto& cell_n = field({{index.at({0u})+c_k[0u], index.at({1u})+c_k[1u]}});
+			auto& info_n = cell_n.template get<"info">();
+			auto info_n_val = info_n({0u});
+			auto k_opp = dfi::opposite_index[k.get()];
+
+			if(info_n_val.get() > 0u){
+				sum_df += dfs_old({k_opp});
+			}
+		}
+		/**
+		 * Get the sum of the unknown dfs and precalculate the direction
+		 */
+		constexpr int known_dir = East ? 1 : -1;
+		auto sum_unknown_dfs = (rho_setting_ - sum_df) * saw::data<FP>{known_dir};
+
+		for(saw::data<sch::UInt64> k{0u}; k < saw::data<sch::UInt64>{Descriptor::Q}; ++k){
+			auto c_k = dfi::directions[k.get()];
+			auto& cell_n = field({{index.at({0u})+c_k[0u], index.at({1u})+c_k[1u]}});
+			auto& info_n = cell_n.template get<"info">();
+			auto info_n_val = info_n({0u});
+			auto k_opp = dfi::opposite_index[k.get()];
+
+			if(info_n_val.get() > 0u){
+				sum_unknown_dfs += dfs_old({k}) * c_k[0u];
+			}
+		}
+
+		auto vel_x = sum_unknown_dfs / rho_setting_;
+
+		if constexpr (East) {
+			dfs_old({2u}) = dfs_old({1u}) + saw::data<FP>{2.0 / 3.0} * rho_setting_ * vel_x;
+			dfs_old({6u}) = dfs_old({5u}) + saw::data<FP>{1.0 / 6.0} * rho_setting_ * vel_x + saw::data<FP>{0.5} * (dfs_old({4u}) - dfs_old({3u}));
+			dfs_old({8u}) = dfs_old({7u}) + saw::data<FP>{1.0 / 6.0} * rho_setting_ * vel_x + saw::data<FP>{0.5} * (dfs_old({3u}) - dfs_old({4u}));
+		}else if constexpr (not East){
+			dfs_old({1u}) = dfs_old({2u}) - saw::data<FP>{2.0 / 3.0} * rho_setting_ * vel_x;
+			dfs_old({5u}) = dfs_old({6u}) - saw::data<FP>{1.0 / 6.0} * rho_setting_ * vel_x + saw::data<FP>{0.5} * (dfs_old({3u}) - dfs_old({4u}));
+			dfs_old({7u}) = dfs_old({8u}) - saw::data<FP>{1.0 / 6.0} * rho_setting_ * vel_x + saw::data<FP>{0.5} * (dfs_old({4u}) - dfs_old({3u}));
+		}
+	}
+};
+}
+}
+
+void set_geometry(saw::data<kel::lbm::sch::CavityFieldD2Q9>& latt){
+	using namespace kel::lbm;
+
+	auto meta = latt.meta();
+
+	/**
+	 * Set ghost
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		info({0u}).set(0u);
+
+	}, {{0u,0u}}, meta);
+
+	/**
+	 * Set wall
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		info({0u}).set(2u);
+
+	}, {{0u,0u}}, meta, {{1u,1u}});
+
+	/**
+	 * Set fluid
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		info({0u}).set(1u);
+
+	}, {{0u,0u}}, meta, {{2u,2u}});
+
+	/**
+	 * Set inflow
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		info({0u}).set(3u);
+
+	}, {{1u,0u}}, {{2u,meta.at({1u})}}, {{0u,2u}});
+
+	/**
+	 * Set outflow
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		info({0u}).set(4u);
+
+	}, {{meta.at({0u})-2u,0u}}, {{meta.at({0u})-1u, meta.at({1u})}}, {{0u,2u}});
+
+	/**
+	 * Set channel wall
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		saw::data<sch::FixedArray<sch::UInt64,2u>> area{{meta.at({0u})-8u, meta.at({1u})-2u}};
+		double ch_width = area.at({1u}).get() * (0.6 * 0.5);
+		double ch_length = area.at({0u}).get() * (0.8 * 0.5);
+
+		saw::data<sch::FixedArray<sch::UInt64,2u>> middle{{meta.at({0u})/2u, meta.at({1u})/2u}};
+
+		double r = ch_length + ch_width * ch_width * 0.25 / ch_length;
+
+		double top_pos = middle.at({1u}).get() + r;
+		double bot_pos = middle.at({1u}).get() - r;
+		double mid = middle.at({0u}).get();
+
+		double r_2 = r*r;
+		double dist_top = (top_pos - index.at({1u}).get());
+		double dist_bot = (bot_pos - index.at({1u}).get());
+		double dist_mid = (mid - index.at({0u}).get());
+
+		double dist_top_sq = dist_top * dist_top + dist_mid * dist_mid;
+		double dist_bot_sq = dist_bot * dist_bot + dist_mid * dist_mid;
+
+		if(dist_top_sq < r_2 or dist_bot_sq < r_2){
+			info({0u}).set(2u);
+		}
+
+	}, {{0u,0u}}, meta, {{4u,1u}});
+}
+
+void set_initial_conditions(saw::data<kel::lbm::sch::CavityFieldD2Q9>& latt){
+	using namespace kel::lbm;
+
+	saw::data<sch::T> rho{1.0};
+	saw::data<sch::FixedArray<sch::T,sch::D2Q9::D>> vel{{0.0,0.0}};
+	auto eq = equilibrium<sch::T,sch::D2Q9>(rho, vel);
+
+	auto meta = latt.meta();
+
+	/**
+	 * Set distribution
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& dfs = cell.template get<"dfs">();
+		auto& dfs_old = cell.template get<"dfs_old">();
+
+		for(saw::data<sch::UInt64> k = 0; k < saw::data<sch::UInt64>{sch::D2Q9::Q}; ++k){
+			dfs(k) = eq.at(k);
+			dfs_old(k) = eq.at(k);
+		}
+
+	}, {{0u,0u}}, meta);
+}
+
+void lbm_step(
+	saw::data<kel::lbm::sch::CavityFieldD2Q9>& latt,
+	uint64_t time_step
+){
+	using namespace kel::lbm;
+	using dfi = df_info<sch::T,sch::D2Q9>;
+
+	bool even_step = ((time_step % 2u) == 0u);
+  /**
+	* 1. Relaxation parameter \tau
+	*/
+	component<sch::T, sch::D2Q9, cmpt::BGK> coll{0.5384};
+	component<sch::T, sch::D2Q9, cmpt::BounceBack> bb;
+	component<sch::T, sch::D2Q9, cmpt::PressureBoundaryRestrictedVelocityTo<true>> inlet{1.01 * dfi::cs2};
+	component<sch::T, sch::D2Q9, cmpt::PressureBoundaryRestrictedVelocityTo<false>> outlet{1.0 * dfi::cs2};
+
+	auto meta = latt.meta();
+
+	/**
+	 * Collision
+	 */
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& info = cell.template get<"info">();
+
+		auto& dfs = cell.template get<"dfs">();
+		auto& dfs_old = cell.template get<"dfs_old">();
+
+		switch(info({0u}).get()){
+			case 1u: {
+				coll.apply(latt, index, time_step);
+				break;
+			}
+			case 2u: {
+				bb.apply(latt, index, time_step);
+				break;
+			}
+			case 3u: {
+				inlet.apply(latt, index, time_step);
+				break;
+			}
+			case 4u: {
+				outlet.apply(latt, index, time_step);
+				break;
+			}
+			default:
+				break;
+		}
+
+	}, {{0u,0u}}, meta);
+
+	// Stream
+	iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+		auto& cell = latt(index);
+		auto& df_new = even_step ? cell.template get<"dfs">() : cell.template get<"dfs_old">();
+		auto& info_new = cell.template get<"info">();
+
+		if(info_new({0u}).get() > 0u){
+			for(uint64_t k = 0u; k < sch::D2Q9::Q; ++k){
+				auto dir = dfi::directions[dfi::opposite_index[k]];
+				auto& cell_dir_old = latt({{index.at({0u})+dir[0],index.at({1u})+dir[1]}});
+
+				auto& df_old = even_step ? cell_dir_old.template get<"dfs_old">() : cell_dir_old.template get<"dfs">();
+
+				df_new({k}) = df_old({k});
+			}
+		}
+	}, {{0u,0u}}, meta);
+}
+
+int main(int argc, char** argv){
+	using namespace kel::lbm;
+	using dfi = df_info<sch::T,sch::D2Q9>;
+
+	std::string_view cfg_file_name = "config.json";
+	if(argc > 1){
+		cfg_file_name = argv[1];
+	}
+
+	auto eo_conf = load_lbm_config<sch::Float64,sch::Descriptor<2u,9u>>(cfg_file_name);
+	if(eo_conf.is_error()){
+		auto& err = eo_conf.get_error();
+		std::cerr<<"[Error]: "<<err.get_category();
+		auto err_msg = err.get_message();
+		if(!err_msg.empty()){
+			std::cerr<<" - "<<err_msg;
+		}
+		std::cerr<<std::endl;
+
+		return err.get_id();
+	}
+
+	auto& conf = eo_conf.get_value();
+
+	converter<sch::Float64> conv {
+		{conf.template get<"delta_x">()},
+		{conf.template get<"delta_t">()}
+	};
+
+	print_lbm_meta<sch::Float64,sch::Descriptor<2u,9u>>(conv, {conf.template get<"kinematic_viscosity">()});
+
+	saw::data<sch::FixedArray<sch::UInt64,sch::D2Q9::D>> dim{{1024u, 128u}};
+	saw::data<sch::CavityFieldD2Q9, saw::encode::Native> lattice{dim};
+	auto meta = lattice.meta();
+
+	/**
+	 * Setup geometry
+	 */
+	set_geometry(lattice);
+
+	{
+
+		saw::data<sch::Array<sch::GeometryStruct<sch::T>, sch::D2Q9::D>> geo{dim};
+
+		iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+			auto& cell = lattice(index);
+			auto& info = cell.template get<"info">();
+
+			geo(index).template get<"info">().set(info({0u}).get());
+		}, {{0u,0u}}, dim);
+
+		std::string vtk_f_name{"tmp/geometry.vtk"};
+		write_vtk_file(vtk_f_name, geo);
+	}
+
+	/**
+	 * Setup DFs
+	 */
+	set_initial_conditions(lattice);
+
+	saw::data<sch::Array<sch::MacroStruct<sch::T,sch::D2Q9::D>,sch::D2Q9::D>> macros{dim};
+
+	for(uint64_t i = 0u; i < 4096u*16u; ++i){
+		bool even_step = ((i % 2u) == 0u);
+
+		{
+			// Stream
+			iterate_over([&](const saw::data<sch::FixedArray<sch::UInt64,2u>>& index){
+				auto& cell = lattice(index);
+				auto& dfs = even_step ? cell.template get<"dfs">() : cell.template get<"dfs_old">();
+
+				auto& rho = macros.at(index).template get<"pressure">();
+				auto& vel = macros.at(index).template get<"velocity">();
+				compute_rho_u<sch::T,sch::D2Q9>(dfs,rho,vel);
+				rho = rho * saw::data<sch::T>{dfi::cs2};
+
+			}, {{0u,0u}}, meta);
+			std::string vtk_f_name{"tmp/poiseulle_2d_"};
+			vtk_f_name += std::to_string(i) + ".vtk";
+			write_vtk_file(vtk_f_name, macros);
+		}
+
+		lbm_step(lattice, i);
+	}
+
+	return 0;
+}
diff --git a/examples/poiseulle_particles_2d.cpp b/examples/poiseulle_particles_2d.cpp
index 3e636f9..d0310e4 100644
--- a/examples/poiseulle_particles_2d.cpp
+++ b/examples/poiseulle_particles_2d.cpp
@@ -3,6 +3,8 @@
 #include "../c++/boundary.hpp"
 #include "../c++/iterator.hpp"
 
+#include "../c++/particle/particle.hpp"
+
 #include <forstio/codec/data.hpp>
 
 namespace kel {
@@ -36,7 +38,8 @@ template<typename Desc>
 using CellStruct = Struct<
 	Member<DfCell<Desc>, "dfs">,
 	Member<DfCell<Desc>, "dfs_old">,
-	Member<CellInfo<Desc>, "info">
+	Member<CellInfo<Desc>, "info">,
+	Member<Cell<UInt8, D2Q9, 1u, 0u, 0u>, "particle_mask">
 >;
 
 template<typename T, uint64_t D>
@@ -335,6 +338,15 @@ int main(int argc, char** argv){
 	saw::data<sch::CavityFieldD2Q9, saw::encode::Native> lattice{dim};
 	auto meta = lattice.meta();
 
+	particle_system<sch::T, sch::D2Q9::D> part_sys;
+	{
+		saw::data<sch::Particle<sch::T, sch::D2Q9::D>> part;
+		auto eov = part_sys.add(std::move(part));
+		if(eov.is_error()){
+			return eov.get_error().get_id();
+		}
+	}
+
 	/**
 	 * Setup geometry
 	 */
-- 
cgit v1.2.3