/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		$β$		$α$	$α_{cs}$	`skew_ID`	`h_1D`
`order`	`h`		$ξ_{stab}$		`hmin`	`hmax`
`hcst`

Definition


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)	$[kg]$
$β$	Quadratic bulk viscosity. Default = 2.0 (Real)
$α$	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_1D`	Smoothing length change based on volume. 5 = 0 (Default) 3D expansion of `h`. = 1 1D expansion of `h`. = 2 `h` is constant. = 3 `h` is computed from max of initial interparticle distance with 3D bounded expansion. (Integer)
`order`	SPH correction order. = -1 Means no correction at all. = 0 (Default) Means order 0 correction. = 1 Means correction up to order 1. (Integer)
`h`	Smoothing length (not considered if `h_opt` = 3). Default: see 1 (Real)	$[m]$
$ξ_{stab}$	Coefficient for solving tensile instability. Default = 0.0 (Real)
`hmin`	Scale factor for the minimum initial smoothing length `h` for `h_1D` = 3. Default = 0.2 (Real)
`hmax`	Scale factor for the maximum initial smoothing length `h` for `h_1D` = 3. Default = 2.0 (Real)
`hcst`	Constant used to compute initial smoothing length `h` for `h_1D` = 3. Default = 1.2 (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                beta               alpha            alpha_cs   skew_ID      h_1D
         1.725149E-4               2E-30               1E-30                   0         0         0
#    order                   h             xi_stab                          hmin                hmax
         0               6.286                   0                             0                   0
#               hcst
                   0 
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|

Comments

Default value for smoothing length if h_1D < 3 is set as:
$h = {(\frac{m_{p} \sqrt{2}}{ρ})}^{\frac{1}{3}}$
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.
If h_1D = 3, the smoothing length is computed with the maximum of intial interparticle distance per part. For each SPH part h is computed for all particles of the part as the maximum over all particles of the part of the distance to the closest neighbor multiply by the scale factor hcst:
$h_{0} = h c s t \cdot m a x (d i s t_{c l o s e s t_n e i g h b o r})$
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 $ξ_{s t a b} = 0.3$ 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:
$h = \frac{1.5 l}{N d i r}$
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_1D = 0, the change in the volume is based on three dimensions:
$\frac{d h}{h} = \frac{1}{3} \frac{d V o l}{V o l} = \frac{1}{3} d i v \vec{V} d t$
If h_1D = 1, the change in the volume is based on one dimension:
$\frac{d h}{h} = \frac{d V o l}{V o l} = d i v \vec{V} d t$
If h_1D = 2, the smoothing length is kept constant during the computation.
If h_1D = 3, the evolution of h is similar to h_1D = 0 with a 3D evolution of the volume but the evolution of h is bounded so that:
$h m i n \cdot h_{0} < h < h m a x \cdot h_{0}$
The particle mass $m_{p}$ is used only if the mass is not defined in the particle element (/SPHCEL).