From f8022a6131126bb43a96908933c8fa0f3fc2f009 Mon Sep 17 00:00:00 2001
From: "Claudius \"keldu\" Holeksa" <mail@keldu.de>
Date: Tue, 5 May 2026 09:58:32 +0200
Subject: Forced Particle LBM

---
 lib/core/c++/fplbm.hpp | 177 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 177 insertions(+)
 create mode 100644 lib/core/c++/fplbm.hpp

(limited to 'lib/core/c++/fplbm.hpp')

diff --git a/lib/core/c++/fplbm.hpp b/lib/core/c++/fplbm.hpp
new file mode 100644
index 0000000..61def6b
--- /dev/null
+++ b/lib/core/c++/fplbm.hpp
@@ -0,0 +1,177 @@
+#pragma once
+
+#include "common.hpp"
+
+namespace kel {
+namespace lbm {
+namespace cmpt {
+struct FpLbm {};
+struct FpLbmOneParticleNoVelocity{};
+}
+
+template<typename T, typename Descriptor, typename Encode>
+class component<T, Descriptor, cmpt::FpLbm, Encode> final {
+private:
+	saw::data<T> relaxation_;
+	saw::data<T> frequency_;
+public:
+	component(typename saw::native_data_type<T>::type relaxation__):
+		relaxation_{{relaxation__}},
+		frequency_{saw::data<T>{1} / relaxation_}
+	{}
+
+	component(const saw::data<T>& relaxation__):
+		relaxation_{relaxation__},
+		frequency_{saw::data<T>{1} / relaxation_}
+	{}
+
+	using Component = cmpt::FpLbm;
+
+
+	template<typename CellFieldSchema, typename MacroFieldSchema>
+	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<MacroFieldSchema,Encode>& macros, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, saw::data<sch::UInt64> time_step) const {
+	// void apply(saw::data<CellFieldSchema, Encode>& field, saw::data<sch::FixedArray<sch::UInt64, Descriptor::D>> index, saw::data<sch::UInt64> time_step){
+		bool is_even = ((time_step.get() % 2) == 0);
+
+		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
+		auto& dfs = dfs_old_f.at(index);
+
+		auto& rho_f = macros.template get<"density">();
+		auto& vel_f = macros.template get<"velocity">();
+
+		saw::data<sch::Scalar<T>>& rho = rho_f.at(index);
+		saw::data<sch::Vector<T,Descriptor::D>>& vel = vel_f.at(index);
+
+		compute_rho_u<T,Descriptor>(dfs_old_f.at(index),rho,vel);
+		auto eq = equilibrium<T,Descriptor>(rho,vel);
+
+		using dfi = df_info<T,Descriptor>;
+
+		auto& force_f = macros.template get<"force">();
+		auto& force = force_f.at(index);
+
+		auto& porosity_f = macros.template get<"porosity">();
+		auto& porosity = porosity_f.at(index);
+
+		saw::data<sch::Scalar<T>> dfi_inv_cs2;
+		dfi_inv_cs2.at({}).set(dfi::inv_cs2);
+
+		for(uint64_t i = 0u; i < Descriptor::Q; ++i){
+			// saw::data<T> ci_min_u{0};
+			saw::data<sch::Vector<T,Descriptor::D>> ci;
+			for(uint64_t d = 0u; d < Descriptor::D; ++d){
+				ci.at({{d}}).set(static_cast<typename saw::native_data_type<T>::type>(dfi::directions[i][d]));
+			}
+			auto ci_dot_u = saw::math::dot(ci,vel);
+
+			// saw::data<sch::Vector<T,Descriptor::D>> F_i;
+			// F_i = f * (c_i - u * ics2  + <c_i,u> * c_i * ics2 * ics2) * w_i;
+			saw::data<sch::Scalar<T>> w;
+			w.at({}).set(dfi::weights[i]);
+
+			auto F_i_d = saw::math::dot(force * w, (ci - vel * dfi_inv_cs2 + ci * ci_dot_u * dfi_inv_cs2 * dfi_inv_cs2 ));
+			/*
+			saw::data<sch::Scalar<T>> F_i_sum;
+			for(uint64_t d = 0u; d < Descriptor::D; ++d){
+				saw::data<sch::Scalar<T>> F_i_d;
+				F_i_d.at({}) = F_i.at({{d}});
+				F_i_sum = F_i_sum + F_i_d;
+			}
+			*/
+
+			dfs.at({i}) = dfs.at({i}) + frequency_ * (eq.at(i) - dfs.at({i}) ) + F_i_d.at({}) * (saw::data<T>{1} - saw::data<T>{0.5f} * frequency_);
+		}
+	}
+};
+
+template<typename T, typename Descriptor, typename Encode>
+class component<T, Descriptor, cmpt::FpLbmOneParticleNoVelocity, Encode> final {
+private:
+	saw::data<T> relaxation_;
+	saw::data<T> frequency_;
+public:
+	component(typename saw::native_data_type<T>::type relaxation__):
+		relaxation_{{relaxation__}},
+		frequency_{saw::data<T>{1} / relaxation_}
+	{}
+
+	component(const saw::data<T>& relaxation__):
+		relaxation_{relaxation__},
+		frequency_{saw::data<T>{1} / relaxation_}
+	{}
+
+	using Component = cmpt::FpLbmOneParticleNoVelocity;
+
+	template<typename CellFieldSchema, typename MacroFieldSchema>
+	void apply(const saw::data<CellFieldSchema, Encode>& field, const saw::data<MacroFieldSchema,Encode>& macros, saw::data<sch::FixedArray<sch::UInt64,Descriptor::D>> index, saw::data<sch::UInt64> time_step) const {
+	// void apply(saw::data<CellFieldSchema, Encode>& field, saw::data<sch::FixedArray<sch::UInt64, Descriptor::D>> index, saw::data<sch::UInt64> time_step){
+		bool is_even = ((time_step.get() % 2) == 0);
+
+		auto& dfs_old_f = (is_even) ? field.template get<"dfs_old">() : field.template get<"dfs">();
+		auto& dfs = dfs_old_f.at(index);
+
+		auto& rho_f = macros.template get<"density">();
+		auto& vel_f = macros.template get<"velocity">();
+		auto& por_f = macros.template get<"porosity">();
+
+		saw::data<sch::Scalar<T>>& rho = rho_f.at(index);
+
+		saw::data<sch::Scalar<T>> half;
+		half.at({}).set(0.5);
+		saw::data<sch::Vector<T,Descriptor::D>>& vel = vel_f.at(index);// + total_force * ( half / rho );
+
+		compute_rho_u<T,Descriptor>(dfs_old_f.at(index),rho,vel);
+		auto eq = equilibrium<T,Descriptor>(rho,vel);
+
+		using dfi = df_info<T,Descriptor>;
+
+		saw::data<sch::Scalar<T>> min_two;
+		min_two.at({}).set(-2);
+
+		auto force = vel * rho * min_two * por_f.at(index);
+
+		saw::data<sch::Scalar<T>> dfi_inv_cs2;
+		dfi_inv_cs2.at({}).set(dfi::inv_cs2);
+
+
+		// auto vel = vel_f.at(index);
+
+		for(uint64_t i = 0u; i < Descriptor::Q; ++i){
+			// saw::data<T> ci_min_u{0};
+			saw::data<sch::Vector<T,Descriptor::D>> ci;
+			for(uint64_t d = 0u; d < Descriptor::D; ++d){
+				ci.at({{d}}).set(static_cast<typename saw::native_data_type<T>::type>(dfi::directions[i][d]));
+			}
+			auto ci_dot_u = saw::math::dot(ci,vel);
+
+			// saw::data<sch::Vector<T,Descriptor::D>> F_i;
+			// F_i = f * ((c_i - u) * ics2  + <c_i,u> * c_i * ics2 * ics2) * w_i;
+			saw::data<sch::Scalar<T>> w;
+			w.at({}).set(dfi::weights[i]);
+
+			/*
+			saw::data<sch::Scalar<T>> F_i_sum;
+			for(uint64_t d = 0u; d < Descriptor::D; ++d){
+				saw::data<sch::Scalar<T>> F_i_d;
+				F_i_d.at({}) = F_i.at({{d}});
+				F_i_sum = F_i_sum + F_i_d;
+			}
+			*/
+			auto term1 = (ci-vel) * dfi_inv_cs2;
+			auto term2 = ci * (ci_dot_u * dfi_inv_cs2 * dfi_inv_cs2);
+
+			auto force_projection = saw::math::dot(term1 + term2, force);
+
+			auto F_i = w * force_projection;
+
+			dfs.at({i}) = dfs.at({i})
+									+ frequency_
+										* (eq.at(i) - dfs.at({i}) )
+									+ F_i.at({})
+										* (saw::data<T>{1} - saw::data<T>{0.5f} * frequency_);
+		}
+	}
+
+};
+}
+}
-- 
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