/PROP/TYPE34 (SPH)

Block Format Keyword Describes SPH property set.

Format

(1)	(2)	(3)	(4)	(5)	(7)	(9)	(10)
/PROP/TYPE34/`prop_ID` or /PROP/SPH/`prop_ID`
`prop_title`
`m`_p		`q`_a		`q`_b	$α_{cs}$	`skew_ID`	`h_ID`
`order`	`h`		$ξ_{stab}$

Definitions

Field	Contents	SI Unit Example
`prop_ID`	Property identifier (Integer, maximum 10 digits)
`prop_title`	Property title (Character, maximum 100 characters)
`m`_p	Mass of the particles. (Real)	$[kg]$
`q`_a	Quadratic bulk viscosity. Default = 2.0 (Real)
`q`_b	Linear bulk viscosity. Default = 1.0 (Real)
$α_{cs}$	Conservative smoothing coefficient. (Real)
`skew_ID`	Skew identifier to define the initial orthotropic directions in the case of `skew_ID` ≠ 0 (means property is orthotropic). (Integer)
`h_ID`	Smoothing length change based on volume. 6 = 0 (Default) 3D expansion of `h` = 1 1D expansion of `h` (Integer)
`order`	SPH correction order. = -1 Means no correction at all. = 0 (Default) Means order 0 correction. = 1 Means correction up to order 1 - not allowed for SPMD parallel version. (Integer)
`h`	Smoothing length. Default: see 2 (Real)	$[m]$
$ξ_{stab}$	Coefficient for solving tensile instability. Default = 0.0 (Real)

Example (Bird Strike)

#RADIOSS STARTER
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/PROP/TYPE34/3000001
BIRD_sphv1 (unit kg_mm_ms) data from Example 49 - Bird Strike on Windshield
#                 mp                  qa                  qb            alpha_cs   skew_ID      h_ID
         1.725149E-4               2E-30               1E-30                   0         0         0
#    order                   h             xi_stab
         0               6.286                   0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

Comments

The recommended SPH cell distribution is face centered cubic which can be created in the HyperMesh SPH panel or hexagonal compact net distribution using a Tcl script available from Altair Connect.
Default value for smoothing length is set as:(1)
$h = {(\frac{m_{p} \sqrt{2}}{ρ})}^{\frac{1}{3}}$

which corresponds to the inter-particles distance when the particles distribution is hexagonal compact.

For face centered cubic and hexagonal compact net distribution, the recommended smoothing length $h$ is the pitch entered when generating the SPH particles.
The kinetic energy absorbed by conservative smoothing of velocities is output as hourglass energy into /TH/PART files.
If $ξ_{stab}$ is not equal to zero, an artificial stress is added to solve the tensile instability, proposed by:
J.J. Monaghan, SPH without a Tensile Instability, Journal of Computational Physics, vol. 159, pp. 290-311, 2000

A value of $ξ_{stab} = 0.3$ is recommended.
If the sphpart_ID is used with Sol2SPH option, (in /PROP/SOLID), $h$ must be input. The mass of the particle can be 0.0 (it is automatically calculated by Radioss). A good value of the smoothing length is:(2)
$h = \frac{1.5 l}{N d i r}$

Where,

$h$

Smoothing length

$l$

Size of the brick elements

$N d i r$

Number of particle per direction for each solid element
The smoothing length on each particle is updated during the computation according to the change in the volume.
If h_ID=0, the change in the volume is based on three dimensions:(3)
$\frac{d h}{h} = \frac{1}{3} \frac{d V o l}{V o l} = \frac{1}{3} d i v \vec{V} d t$

If h_ID=1, the change in the volume is based on one dimension:(4)
$\frac{d h}{h} = \frac{d V o l}{V o l} = d i v \vec{V} d t$