/LOAD/PFLUID

Block Format Keyword This entry provides a simple way to simulate hydrodynamic fluid pressure on a structure. The fluid pressure is calculated according to the specified fluid velocity, orientation of the structural surface against the fluid vector and the height of the fluid column above the surface of the structure.

Format


(1)	(2)	(3)	(5)
/LOAD/PFLUID/`load_ID`/`unit_ID`
`load_title`
`surf_ID`	`sens_ID`
`fct_hsp`		`Ascalex_hsp`	`Fscaley_hsp`
`Dir_hsp`	`frahsp_ID`
`fct_pc`		`Ascalex_pc`	`Fscaley_pc`
`fct_vel`		`Ascalex_vel`	`Fscaley_vel`
`Dir_vel`	`fravel_ID`

Definition


Field	Contents	SI Unit Example
`load_ID`	Load block identifier. (Integer, maximum 10 digits)
`unit_ID`	(Optional) Unit identifier. (Integer, maximum 10 digits)
`load_title`	Load block title. (Character, maximum 100 characters)
`surf_ID`	Surface identifier. (Integer)
`sens_ID`	Sensor identifier. (Integer)
`fct_hsp`	Hydro-static pressure as a function of the fluid column height above the structural surface. (Integer)
`Ascalex_hsp`	Abscissa scale factor for `fct_hsp`. Default = 1.0 (Real)	$[s]$
`Fscaley_hsp`	Ordinate scale factor for `fct_hsp`. Default = 1.0 (Real)	$[Pa]$
`Dir_hsp`	Vertical (gravitational) direction of the water column above the structural surface (input X, Y or Z). (Text)
`frahsp_ID`	Frame identifier for the vertical (gravitational) direction of the water column above the structural surface. (Integer)
`fct_pc`	Hydrodynamic drag coefficient as a function of time. 4 (Integer)
`Ascalex_pc`	Abscissa scale factor for `fct_pc`. Default = 1.0 (Real)	$[s]$
`Fscaley_pc`	Ordinate scale factor for `fct_pc`. Default = 1.0 (Real)	$[\frac{kg}{m^{3}}]$
`fct_vel`	Fluid velocity as a function of time. (Integer)
`Ascalex_vel`	Abscissa scale factor for `fct_vel`. Default = 1.0 (Real)	$[s]$
`Fscaley_vel`	Ordinate scale factor for `fct_vel`. Default = 1.0 (Real)	$[\frac{m}{s}]$
`Dir_vel`	Direction of fluid velocity (input X, Y or Z). (Text)
`fravel_ID`	Frame identifier for the fluid velocity direction. (Integer)

Example (Wind Effect)

In this example, /LOAD/PFLUID is used to simulate wind (with velocity 15[mm/ms]) effect on textile.

#RADIOSS STARTER
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/UNIT/1
unit for load
#              MUNIT               LUNIT               TUNIT
                 kg                  mm                  ms
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/LOAD/PFLUID/1/1
Wind effect
#  surf_ID   sens_ID
         8         0
#  fct_hsp                   Ascalex_hsp         Fscaley_hsp
         0                             0                   0
#  Dir_hsp frahsp_ID
                   0
#   fct_pc                    Ascalex_pc          Fscaley_pc
         2                             0                   2
#  fct_vel                   Ascalex_vel         Fscaley_vel
         3                             0                  15
#  Dir_vel fravel_ID
         Y         0
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/2
Air density
#                  X                   Y
                   0              1.2E-9
                1000              1.2E-9
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
/FUNCT/3
Air velocity
#                  X                   Y
                   0                   1
                1000                   1
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
#ENDDATA

Comments

The fluid pressure applied to each element of the structural surface is computed as:
$P = ρ g h + \frac{V^{2} (t) (ρ D (t))}{2}$
Where,

$ρ$

Fluid density

$g$

Acceleration due to gravity

$h$

Height of the water column above an element of the structural surface

$V (t)$

Relative fluid velocity which is normal to the element of the structural surface

$D (t)$

Drag coefficient for complete structural surface

The value of the drag coefficient depends on the shape of the cross-section of the body in the direction of fluid flow (Figure 2).

Figure 2. Drag Coefficient Values for Different Shapes
The value of hydrostatic pressure ( $ρ g h$ ) as a function of fluid column height ( $h$ ) above the structural surface is stated using the function fct_hsp. If this is not defined (=0), the effect is not accounted for (fct_hsp(altitude)=0).
Hydrodynamic pressure is calculated with respect to the relative orientation of the fluid vector and the element normal.
$V (t) = | ((V_{f l u i d} - V_{e l e m e n t}), n) |$
Where,

$V_{f l u i d}$

Specified fluid velocity (fct_vel(t)). If not defined (=0), the effect of fluid velocity is not accounted for ( $V (t)$ = 0)

$V_{e l e m e n t}$

Element velocity

$n$

Element normal
fct_pc defines the value of $ρ D (t)$ as a function of time. If this is not defined, the effect of fluid velocity is not accounted for.