Soft-sphere Hertz–Mindlin DEM (reference force model) for SPHERES. More...

#include <Kokkos_Core.hpp>
#include <Kokkos_Sort.hpp>
#include "contact_preprocessing.hpp"
#include "narrowphase.hpp"
#include "particles.hpp"

Namespaces
namespace	peclet

namespace	peclet::dem

Functions
void	peclet::dem::hertzPairEMu (int matA, int matB, PairTableView pairTable, float eGlobal, float muGlobal, float &e, float &mu)
	Pairwise (e, mu) lookup shared with the narrowphase convention: pair table if present, global fallback otherwise.

float	peclet::dem::hertzBetaD (float e)
	Restitution -> damping ratio beta_d = ln e / sqrt(ln^2 e + pi^2) (e in (0, 1]; e <= 0 -> -1, the critically-damped limit used by LIGGGHTS for e -> 0).

F3	peclet::dem::hertzForce (float delta, F3 nhat, F3 vrel, float rStar, float mStar, float eStar, float gStar, float e, float mu, float dt, F3 &xi)
	One Hertz–Mindlin force evaluation for a sphere-sphere or sphere-wall contact.

void	peclet::dem::hertzPairForcesKokkos (Kokkos::View< const int [2], CpMem > pairs, int numPairs, Kokkos::View< const float [3], CpMem > pos, Kokkos::View< const float [3], CpMem > vel, Kokkos::View< const float [3], CpMem > angVel, Kokkos::View< const float , CpMem > rad, Kokkos::View< const float , CpMem > invMass, MatIdView matId, PairTableView pairTable, float eGlobal, float muGlobal, Kokkos::View< const float , CpMem > hertzE, Kokkos::View< const float , CpMem > hertzNu, float dt, Kokkos::View< float [3], CpMem > xi, Kokkos::View< float [3], CpMem > force, Kokkos::View< float *[3], CpMem > torque)
	Cached-pair forces: overlap from current positions; history resets when a cached pair is currently separated.

void	peclet::dem::hertzWallForcesKokkos (Kokkos::View< const int , CpMem > candSlots, int numCand, Kokkos::View< const WallSdf , CpMem > walls, GridView wallGrid, Kokkos::View< const float [3], CpMem > pos, Kokkos::View< const float [3], CpMem > vel, Kokkos::View< const float [3], CpMem > angVel, Kokkos::View< const float , CpMem > rad, Kokkos::View< const float , CpMem > invMass, MatIdView matId, PairTableView pairTable, float eGlobal, float muGlobal, Kokkos::View< const float , CpMem > hertzE, Kokkos::View< const float , CpMem > hertzNu, float dt, Kokkos::View< float [3], CpMem > xiWall, int maxWalls, Kokkos::View< float [3], CpMem > force, Kokkos::View< float [3], CpMem > torque, Kokkos::View< const float [4], CpMem > quat={}, Kokkos::View< const float , CpMem > scale={}, ScalarI shapeId={}, Kokkos::View< const ShapeDesc , CpMem > shapes={}, ShellView shell={}, float globalScale=1.0f, float contactRadiusFrac=0.5f, bool hasShapes=false, Kokkos::View< float , CpMem > snWall={})
	SDF-wall forces (per particle x wall).

int	peclet::dem::hertzBuildWallCandidatesKokkos (int numReal, int numWalls, Kokkos::View< const WallSdf , CpMem > walls, GridView wallGrid, Kokkos::View< const float [3], CpMem > pos, Kokkos::View< const float , CpMem > rad, float skin, Kokkos::View< int , CpMem > outSlots, Kokkos::View< int, CpMem > outCount)
	Build the wall candidate list: particles within (radius + skin) of any wall's zero level.

void	peclet::dem::hertzIntegrateKokkos (int numReal, Kokkos::View< float [3], CpMem > force, Kokkos::View< float [3], CpMem > torque, Kokkos::View< const float , CpMem > invMass, Kokkos::View< const float [3], CpMem > invInertia, F3 gravity, float dt, Kokkos::View< float [3], CpMem > vel, Kokkos::View< float [3], CpMem > angVel, Kokkos::View< float [3], CpMem > pos, Kokkos::View< float [4], CpMem > quat={}, bool integrateOrientation=false)
	Symplectic-Euler kick-drift (MUSEN-style) + displacement tracking for the Verlet rebuild.

float	peclet::dem::hertzMaxDisp2Kokkos (int numReal, Kokkos::View< const float [3], CpMem > pos, Kokkos::View< const float [3], CpMem > refPos)
	Max squared displacement since the last pair build (called only at rebuild checks – keeping this out of the integrate kernel avoids a per-step single-address atomic).

void	peclet::dem::hertzShapePairForcesKokkos (Kokkos::View< const int [2], CpMem > pairs, int numPairs, Kokkos::View< const float [3], CpMem > pos, Kokkos::View< const float [4], CpMem > quat, Kokkos::View< const float [3], CpMem > vel, Kokkos::View< const float [3], CpMem > angVel, Kokkos::View< const float , CpMem > scale, ScalarI shapeId, Kokkos::View< const ShapeDesc , CpMem > shapes, ShellView shell, GridView sdfGrid, float globalScale, float contactRadiusFrac, Kokkos::View< const float , CpMem > invMass, MatIdView matId, PairTableView pairTable, float eGlobal, float muGlobal, Kokkos::View< const float , CpMem > hertzE, Kokkos::View< const float , CpMem > hertzNu, float dt, Kokkos::View< float [3], CpMem > xi, Kokkos::View< float , CpMem > snPrev, Kokkos::View< float [3], CpMem > force, Kokkos::View< float [3], CpMem > torque)
	Non-spherical pairs: per-point Hertz springs over A's point shell against B's SDF (the same one-sided sampling convention as the narrowphase), ONE Mindlin patch history per pair.

Detailed Description

Soft-sphere Hertz–Mindlin DEM (reference force model) for SPHERES.

The benchmark contact model of Dosta et al. (2024): viscoelastic Hertz normal force with restitution-matched damping + "no-slip" Mindlin tangential spring with history, Coulomb-clamped (LIGGGHTS gran model hertz tangential history formulas). This is an explicit force model — time step limited by the Rayleigh time — living beside the impulse (XPBD/NSCD) solver as a physics reference and cross-check. Spheres only, non-periodic domains, SDF walls (no planes).

Structure: a cached Verlet pair list (broadphase margin = skin, rebuilt when any particle has moved skin/2) carries the per-pair tangential history xi through its slots; on rebuild the history is carried over by pair key. Wall contacts are evaluated per particle per wall each step with per-(particle, wall) history. The inner time loop runs device-side per call.

Definition in file solver_hertz.hpp.

Namespaces

Functions

Detailed Description