rustytorch/crates/specialized/rtx-cfd/src/turbulence/smagorinsky_gpu.rs

//! GPU-accelerated Smagorinsky LES turbulence model
//!
//! This module provides CUDA-accelerated implementation of the Smagorinsky
//! subgrid-scale model for Large Eddy Simulation (LES).

use super::SmagorinskyConstants;
use crate::kernels::CudaKernelManager;
use crate::{CfdConfig, CfdError, CfdResult};
use cudarc::driver::{CudaModule, CudaSlice, LaunchConfig, PushKernelArg};
use std::sync::Arc;

/// GPU memory buffers for Smagorinsky model
struct SmagorinskyGpuBuffers {
    /// Grid dimensions
    nx: usize,
    ny: usize,
    nz: usize,

    /// Filter width
    delta: CudaSlice<f32>,

    /// Velocity gradients
    dudx: CudaSlice<f32>,
    dudy: CudaSlice<f32>,
    dudz: CudaSlice<f32>,
    dvdx: CudaSlice<f32>,
    dvdy: CudaSlice<f32>,
    dvdz: CudaSlice<f32>,
    dwdx: CudaSlice<f32>,
    dwdy: CudaSlice<f32>,
    dwdz: CudaSlice<f32>,

    /// Strain rate tensor magnitude |S|
    strain_rate: CudaSlice<f32>,

    /// Subgrid-scale viscosity
    sgs_viscosity: CudaSlice<f32>,

    /// Temporary arrays
    temp1: CudaSlice<f32>,
    temp2: CudaSlice<f32>,
}

/// GPU-accelerated Smagorinsky SGS model for LES
pub struct SmagorinskyGpuModel {
    /// GPU kernel manager
    kernel_manager: Arc<CudaKernelManager>,
    /// Model constants
    constants: SmagorinskyConstants,
    /// Smagorinsky CUDA module
    smagorinsky_module: Option<Arc<CudaModule>>,
    /// GPU memory buffers
    gpu_buffers: Option<SmagorinskyGpuBuffers>,
}

impl SmagorinskyGpuModel {
    /// Create new Smagorinsky GPU model
    pub fn new(config: &CfdConfig) -> CfdResult<Self> {
        let kernel_manager = Arc::new(CudaKernelManager::new(config)?);

        Ok(Self {
            kernel_manager,
            constants: SmagorinskyConstants::standard(),
            smagorinsky_module: None,
            gpu_buffers: None,
        })
    }

    /// Initialize model with grid dimensions
    pub fn initialize(&mut self, nx: usize, ny: usize, nz: usize) -> CfdResult<()> {
        // Load Smagorinsky kernels
        self.load_smagorinsky_kernels()?;

        // Allocate GPU buffers
        self.allocate_gpu_buffers(nx, ny, nz)?;

        Ok(())
    }

    /// Load and compile Smagorinsky CUDA kernels
    fn load_smagorinsky_kernels(&mut self) -> CfdResult<()> {
        // In real implementation, would compile or load PTX for Smagorinsky kernels
        self.smagorinsky_module = Some(
            self.kernel_manager
                .get_module("smagorinsky_kernels")?
                .clone(),
        );
        Ok(())
    }

    /// Allocate GPU memory buffers
    fn allocate_gpu_buffers(&mut self, nx: usize, ny: usize, nz: usize) -> CfdResult<()> {
        let n = nx * ny * nz;

        let buffers = SmagorinskyGpuBuffers {
            nx,
            ny,
            nz,
            delta: self.kernel_manager.allocate_f32(n)?,
            dudx: self.kernel_manager.allocate_f32(n)?,
            dudy: self.kernel_manager.allocate_f32(n)?,
            dudz: self.kernel_manager.allocate_f32(n)?,
            dvdx: self.kernel_manager.allocate_f32(n)?,
            dvdy: self.kernel_manager.allocate_f32(n)?,
            dvdz: self.kernel_manager.allocate_f32(n)?,
            dwdx: self.kernel_manager.allocate_f32(n)?,
            dwdy: self.kernel_manager.allocate_f32(n)?,
            dwdz: self.kernel_manager.allocate_f32(n)?,
            strain_rate: self.kernel_manager.allocate_f32(n)?,
            sgs_viscosity: self.kernel_manager.allocate_f32(n)?,
            temp1: self.kernel_manager.allocate_f32(n)?,
            temp2: self.kernel_manager.allocate_f32(n)?,
        };

        self.gpu_buffers = Some(buffers);
        Ok(())
    }

    /// Compute filter width on GPU
    pub fn compute_filter_width(&mut self, dx: f32, dy: f32, dz: f32) -> CfdResult<()> {
        let buffers = self
            .gpu_buffers
            .as_mut()
            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;

        let module = self
            .smagorinsky_module
            .as_ref()
            .ok_or_else(|| CfdError::gpu_error("Smagorinsky module not loaded"))?;
        let func = module.load_function("compute_filter_width").map_err(|e| {
            CfdError::gpu_error(&format!("Failed to get filter width kernel: {}", e))
        })?;

        let grid_dim_x = (buffers.nx as u32 + 7) / 8;
        let grid_dim_y = (buffers.ny as u32 + 7) / 8;
        let grid_dim_z = (buffers.nz as u32 + 7) / 8;

        let config = LaunchConfig {
            grid_dim: (grid_dim_x, grid_dim_y, grid_dim_z),
            block_dim: (8, 8, 8),
            shared_mem_bytes: 0,
        };

        unsafe {
            unsafe {
                self.kernel_manager
                    .stream()
                    .launch_builder(&func)
                    .arg(&mut buffers.delta)
                    .arg(&dx)
                    .arg(&dy)
                    .arg(&dz)
                    .arg(&(buffers.nx as i32))
                    .arg(&(buffers.ny as i32))
                    .arg(&(buffers.nz as i32))
                    .launch(config)
                    .map_err(|e| {
                        CfdError::gpu_error(&format!("Filter width kernel launch failed: {}", e))
                    })?;
            }
        }

        self.kernel_manager.synchronize()?;
        Ok(())
    }

    /// Compute SGS viscosity using Smagorinsky model
    pub fn compute_sgs_viscosity(
        &mut self,
        u: &CudaSlice<f32>,
        v: &CudaSlice<f32>,
        w: &CudaSlice<f32>,
        dx: f32,
        dy: f32,
        dz: f32,
    ) -> CfdResult<()> {
        // Step 1: Compute velocity gradients
        self.compute_velocity_gradients(u, v, w, dx, dy, dz)?;

        // Step 2: Compute strain rate magnitude
        self.compute_strain_rate_magnitude()?;

        // Step 3: Compute SGS viscosity = (Cs * delta)^2 * |S|
        self.compute_sgs_viscosity_from_strain()?;

        Ok(())
    }

    /// Compute velocity gradients on GPU
    fn compute_velocity_gradients(
        &mut self,
        u: &CudaSlice<f32>,
        v: &CudaSlice<f32>,
        w: &CudaSlice<f32>,
        dx: f32,
        dy: f32,
        dz: f32,
    ) -> CfdResult<()> {
        let buffers = self
            .gpu_buffers
            .as_mut()
            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;

        let module = self
            .smagorinsky_module
            .as_ref()
            .ok_or_else(|| CfdError::gpu_error("Smagorinsky module not loaded"))?;
        let func = module
            .load_function("compute_velocity_gradients")
            .map_err(|e| {
                CfdError::gpu_error(&format!("Failed to get velocity gradients kernel: {}", e))
            })?;

        let grid_dim_x = (buffers.nx as u32 + 7) / 8;
        let grid_dim_y = (buffers.ny as u32 + 7) / 8;
        let grid_dim_z = (buffers.nz as u32 + 7) / 8;

        let config = LaunchConfig {
            grid_dim: (grid_dim_x, grid_dim_y, grid_dim_z),
            block_dim: (8, 8, 8),
            shared_mem_bytes: 0,
        };

        unsafe {
            unsafe {
                self.kernel_manager
                    .stream()
                    .launch_builder(&func)
                    .arg(u)
                    .arg(v)
                    .arg(w)
                    .arg(&mut buffers.dudx)
                    .arg(&mut buffers.dudy)
                    .arg(&mut buffers.dudz)
                    .arg(&mut buffers.dvdx)
                    .arg(&mut buffers.dvdy)
                    .arg(&mut buffers.dvdz)
                    .arg(&mut buffers.dwdx)
                    .arg(&mut buffers.dwdy)
                    .arg(&mut buffers.dwdz)
                    .arg(&dx)
                    .arg(&dy)
                    .arg(&dz)
                    .arg(&(buffers.nx as i32))
                    .arg(&(buffers.ny as i32))
                    .arg(&(buffers.nz as i32))
                    .launch(config)
                    .map_err(|e| {
                        CfdError::gpu_error(&format!(
                            "Velocity gradients kernel launch failed: {}",
                            e
                        ))
                    })?;
            }
        }

        Ok(())
    }

    /// Compute strain rate magnitude |S|
    fn compute_strain_rate_magnitude(&mut self) -> CfdResult<()> {
        let buffers = self
            .gpu_buffers
            .as_mut()
            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;

        let module = self
            .smagorinsky_module
            .as_ref()
            .ok_or_else(|| CfdError::gpu_error("Smagorinsky module not loaded"))?;
        let func = module
            .load_function("compute_strain_rate_magnitude")
            .map_err(|e| {
                CfdError::gpu_error(&format!("Failed to get strain rate kernel: {}", e))
            })?;

        let grid_dim_x = (buffers.nx as u32 + 7) / 8;
        let grid_dim_y = (buffers.ny as u32 + 7) / 8;
        let grid_dim_z = (buffers.nz as u32 + 7) / 8;

        let config = LaunchConfig {
            grid_dim: (grid_dim_x, grid_dim_y, grid_dim_z),
            block_dim: (8, 8, 8),
            shared_mem_bytes: 0,
        };

        unsafe {
            unsafe {
                self.kernel_manager
                    .stream()
                    .launch_builder(&func)
                    .arg(&buffers.dudx)
                    .arg(&buffers.dudy)
                    .arg(&buffers.dudz)
                    .arg(&buffers.dvdx)
                    .arg(&buffers.dvdy)
                    .arg(&buffers.dvdz)
                    .arg(&buffers.dwdx)
                    .arg(&buffers.dwdy)
                    .arg(&buffers.dwdz)
                    .arg(&mut buffers.strain_rate)
                    .arg(&(buffers.nx as i32))
                    .arg(&(buffers.ny as i32))
                    .arg(&(buffers.nz as i32))
                    .launch(config)
                    .map_err(|e| {
                        CfdError::gpu_error(&format!("Strain rate kernel launch failed: {}", e))
                    })?;
            }
        }

        Ok(())
    }

    /// Compute SGS viscosity from strain rate
    fn compute_sgs_viscosity_from_strain(&mut self) -> CfdResult<()> {
        let buffers = self
            .gpu_buffers
            .as_mut()
            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;

        let module = self
            .smagorinsky_module
            .as_ref()
            .ok_or_else(|| CfdError::gpu_error("Smagorinsky module not loaded"))?;
        let func = module.load_function("compute_sgs_viscosity").map_err(|e| {
            CfdError::gpu_error(&format!("Failed to get SGS viscosity kernel: {}", e))
        })?;

        let grid_dim_x = (buffers.nx as u32 + 7) / 8;
        let grid_dim_y = (buffers.ny as u32 + 7) / 8;
        let grid_dim_z = (buffers.nz as u32 + 7) / 8;

        let config = LaunchConfig {
            grid_dim: (grid_dim_x, grid_dim_y, grid_dim_z),
            block_dim: (8, 8, 8),
            shared_mem_bytes: 0,
        };

        unsafe {
            unsafe {
                self.kernel_manager
                    .stream()
                    .launch_builder(&func)
                    .arg(&buffers.strain_rate)
                    .arg(&buffers.delta)
                    .arg(&mut buffers.sgs_viscosity)
                    .arg(&self.constants.cs)
                    .arg(&(buffers.nx as i32))
                    .arg(&(buffers.ny as i32))
                    .arg(&(buffers.nz as i32))
                    .launch(config)
                    .map_err(|e| {
                        CfdError::gpu_error(&format!("SGS viscosity kernel launch failed: {}", e))
                    })?;
            }
        }

        self.kernel_manager.synchronize()?;
        Ok(())
    }

    /// Get SGS viscosity field from GPU
    pub fn get_sgs_viscosity(&self) -> CfdResult<Vec<f32>> {
        let buffers = self
            .gpu_buffers
            .as_ref()
            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;

        let n = buffers.nx * buffers.ny * buffers.nz;
        let mut sgs_viscosity_host = vec![0.0f32; n];

        self.kernel_manager
            .stream()
            .memcpy_dtoh(&buffers.sgs_viscosity, &mut sgs_viscosity_host)
            .map_err(|e| {
                CfdError::gpu_error(&format!("Failed to copy SGS viscosity from GPU: {}", e))
            })?;

        self.kernel_manager.synchronize()?;
        Ok(sgs_viscosity_host)
    }
}