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POWDER_BURN_SHAPE_FUNCTION

Material properties

*POWDER_BURN_SHAPE_FUNCTION
"Optional title"
coid
pid, cid

Parameter definition

Variable
Description
coid
Command ID
pid
Part ID
cid
ID of CURVE defining grain area versus burn distance

Description

This command is used to prescribe the propellant grain area versus burn distance when using MAT_POWDER_BURN. Default area is based on the FE mesh. It is sometimes difficult, or computationally too demanding, to model and resolve the true geometry. This command then offers an alternative.

Example

Detailed versus simplified grain

Two propellant grains are ignited inside a small closed chamber. Both grains represent the same geometry (single perforated cylinder). Grain 1 is modelled with its correct geometry, which requires several elements, whereas Grain 2 is represented by a single hexahedron element. POWDER_BURN_SHAPE_FUNCTION is used to prescribe the grain area versus burn distance. This ensures correct mass and energy release rates, even though the physical shape and volume of the grain are not correct.

*UNIT_SYSTEM SI *PARAMETER D = 0.005, "Grain diameter" d = 0.0005, "Grain hole diameter" h = 0.0035, "Grain height" x1 = 0.5*min(%h, %D-%d), "Max burn distance" A0 = pi*(%D+%d)*%h + pi/2*(%D^2-%d^2), "Initial grain area" A1 = pi*(%D+%d)*(%h-2*%x1) + pi/2*((%D-2*%x1)^2 + (%d+2*%x1)^2), "Grain area at max burn distance" # # --- TIME --- # *TIME 0.01 # # --- MESH --- # *COMPONENT_PIPE "Detailed grain" 1, 1, 10, 40, 4 [-%D], 0, 0, [-%D], 0, [%h], [%d/2], [%D/2] *COMPONENT_BOX "Simplified grain" 2, 2, 1, 1, 1 [%D/2], [-%h/2], 0, [%D/2+%h], [%h/2], [%h] # # --- MATERIAL --- # *MAT_POWDER_BURN "Propellant" 1, 1500.0 1000.0, 1.3, 4.0e6, 0, 100, 600.0, 0.0, 1.0e-4 *FUNCTION "Burn rate" 100 0.01 * (p / 1.0e6)^0.8 # *POWDER_BURN_SHAPE_FUNCTION "Simplified grain" 2 2, 101 *CURVE "Grain area versus burn distance" 101 0.0, [%A0] [0.999*%x1], [%A1] [1.001*%x1], 0.0 # # --- PART --- # *PART "Detailed grain" 1, 1 "Simplified grain" 2, 1 # # --- BC --- # *BC_MOTION "Hold grains" 1 G, 1, XYZ # # --- CFD --- # *CFD_DOMAIN 1 ALL, 0, 0.0003, 0, 1 -0.01, -0.01, -0.01, 0.01, 0.01, 0.01 1, 1, 1, 1, 1, 1 *CFD_GAS "Hot igniting gases" 1 USER, 1 10.0, 1.4, 2.0e7, 700.0 *GEOMETRY_BOX 1 -0.01, -0.01, -0.01, 0.01, 0.01, 0.01 *END