Sensitivity Analysis of the DEM Model Numerical Parameters on the Value of the Angle of Repose of Lunar Regolith Analogs

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Figure 6.

Particles’ material parameters

Parameter	Value
Density (bulk density) (kg/m3)	2900 (1740)
Young's modulus (MPa)	45
Poisson's ratio (-)	0.5

AR for different DEM contact models

Tangential forces models	Normal forces models
	Hertzian spring dashpot	Linear spring dashpot	Hysteretic linear spring
Mindlin–Deresiewicz	42.58	-	-
Linear spring Coulomb limit	43.00	45.03	41.40

Sensitivity analysis results

Friction coefficient	Adhesive distance (m)	Force fraction	Restitution coefficient	Rolling resistance	Tangential stiffness ratio	Angle of repose (deg)
0.2	0.0011	0.16	0.34	0.32	0.52	33.84
0.2	0.0011	0.16	0.34	0.32	1	34.45
0.8	0.0005	0.16	0.22	0.2	0.2	35.88
0.2	0.0005	0.4	0.16	0.68	0.68	36.42
0.2	0.0009	0.28	0.28	0.68	0.36	37.40
0.2	0.0005	0.22	0.34	0.68	0.68	37.40
0.2	0.0011	0.16	0.34	0.68	0.52	37.87
0.2	0.0005	0.4	0.34	0.68	0.68	38.47
0.2	0.0015	0.1	0.1	0.68	0.84	38.47
0.8	0.0011	0.16	0.22	0.2	0.2	38.69
0.44	0.0005	0.22	0.22	0.32	0.52	39.97
0.8	0.0011	0.16	0.22	0.2	0.68	40.73
0.44	0.0005	0.22	0.22	0.32	1	41.63
0.56	0.0009	0.28	0.28	0.32	0.36	41.63
0.32	0.0011	0.4	0.22	0.2	0.68	41.86
0.2	0.0011	0.4	0.16	0.68	0.68	42.43
0.32	0.0011	0.4	0.22	0.2	0.2	42.55
0.32	0.0011	0.4	0.4	0.2	0.68	42.99
0.44	0.0005	0.4	0.22	0.32	1	43.69
0.8	0.0005	0.4	0.22	0.32	1	44.26
0.44	0.0011	0.22	0.22	0.32	0.52	45.72
0.2	0.0015	0.28	0.1	0.68	0.84	46.94
0.8	0.0005	0.34	0.4	0.56	0.2	47.00
0.2	0.0015	0.28	0.28	0.68	0.84	47.20
0.2	0.0015	0.28	0.28	0.68	0.36	47.54
0.68	0.0011	0.4	0.4	0.56	0.68	47.95
0.44	0.0005	0.34	0.4	0.56	0.2	48.32
0.32	0.0011	0.4	0.4	0.56	0.68	48.56
0.56	0.0011	0.16	0.34	0.68	0.52	48.68
0.2	0.0015	0.4	0.34	0.44	0.36	49.37
0.68	0.0005	0.22	0.4	0.56	0.68	49.69
0.8	0.0005	0.16	0.22	0.56	0.2	49.86
0.56	0.0011	0.4	0.16	0.32	0.2	50.49
0.56	0.0009	0.4	0.16	0.44	0.84	51.93
0.56	0.0005	0.34	0.16	0.68	0.52	52.16
0.56	0.0015	0.4	0.34	0.44	0.84	52.42
0.56	0.0009	0.28	0.28	0.68	0.36	52.70
0.56	0.0009	0.22	0.16	0.8	0.84	53.48
0.8	0.0005	0.34	0.22	0.56	0.2	53.65
0.56	0.0009	0.4	0.34	0.44	0.84	54.97
0.8	0.0005	0.4	0.22	0.68	1	55.15
0.56	0.0009	0.4	0.16	0.8	0.84	57.67
0.56	0.0015	0.4	0.34	0.44	0.36	58.06
0.56	0.0011	0.16	0.16	0.68	0.52	59.11
0.68	0.0011	0.22	0.4	0.56	0.68	59.65
0.8	0.0005	0.4	0.4	0.68	1	61.26
0.56	0.0011	0.4	0.16	0.68	0.2	61.70
0.56	0.0011	0.4	0.16	0.68	0.68	63.71
0.56	0.0011	0.34	0.16	0.68	0.52	64.06

Materials’ interaction parameters used in the grain size and contact model analyses

Parameter	Particle–particle	Particle–boundary
Static friction (−)	0.7	0.7
Dynamic friction (−)	0.7	0.7
Tangential stiffness ratio (−)	1	1
Adhesive distance (m)	0.0001	0.0001
Force fraction (−)	0.2	0
Restitution coefficient (−)	0.2	0.3

Ranges of variability of the contact model parameters used in the sensitivity analysis

	Parameter	Lower limit	Upper limit
p1	Friction coefficient (f)	0.2	0.5
p2	Adhesive distance (δadh)	0.0005	0.0015
p3	Force fraction (fadh)	0.1	0.4
p4	Restitution coefficient (ɛ)	0.1	0.4
p5	Rolling resistance (fr)	0.2	0.8
p6	Tangential stiffness ratio (rK)	0.2	1.0

Computation time for different DEM contact models

Tangential forces models	Normal forces models
	Hertzian spring dashpot	Linear spring dashpot	Hysteretic linear spring
Mindlin–Deresiewicz	117.73	-	-
Linear spring Coulomb limit	122.93	181.41	237.09