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) (4) (5) (6) (7) (8) (9) (10)
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

## Definitions

Field Contents SI Unit Example

(Integer, maximum 10 digits)

unit_ID Unit Identifier.

(Integer, maximum 10 digits)

(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)

$\left[\text{s}\right]$
Fscaley_hsp Ordinate scale factor for fct_hsp.

Default = 1.0 (Real)

$\left[\text{Pa}\right]$
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)

$\left[\text{s}\right]$
Fscaley_pc Ordinate scale factor for fct_pc.

Default = 1.0 (Real)

$\left[\frac{\text{kg}}{{\text{m}}^{\text{3}}}\right]$
fct_vel Fluid velocity as a function of time.

(Integer)

Ascalex_vel Abscissa scale factor for fct_vel.

Default = 1.0 (Real)

$\left[\text{s}\right]$
Fscaley_vel Ordinate scale factor for fct_vel.

Default = 1.0 (Real)

$\left[\frac{\text{m}}{\text{s}}\right]$
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
#              MUNIT               LUNIT               TUNIT
kg                  mm                  ms
#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|
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

1. The fluid pressure applied to each element of the structural surface is computed as:(1)
$P=\rho gh+\frac{{\mathrm{V}}^{2}\left(t\right)\left(\rho \mathrm{D}\left(t\right)\right)}{2}$
Where,
$\rho$
Fluid density
$g$
Acceleration due to gravity
$h$
Height of the water column above an element of the structural surface
$\mathrm{V}\left(t\right)$
Relative fluid velocity which is normal to the element of the structural surface
$\mathrm{D}\left(t\right)$
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).
2. The value of hydrostatic pressure ( $\rho gh$ ) 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).
3. Hydrodynamic pressure is calculated with respect to the relative orientation of the fluid vector and the element normal.(2)
$\mathrm{V}\left(t\right)=|\left(\left({V}_{fluid}-{V}_{element}\right),n\right)|$
Where,
${V}_{fluid}$
Specified fluid velocity (fct_vel(t)). If not defined (=0), the effect of fluid velocity is not accounted for ( $\mathrm{V}\left(t\right)$ = 0)
${V}_{element}$
Element velocity
$n$
Element normal
4. fct_pc defines the value of $\rho \mathrm{D}\left(t\right)$ as a function of time. If this is not defined, the effect of fluid velocity is not accounted for.