/EBCS/PRES
Block Format Keyword Describes the elementary boundary condition to imposed density and pressure.
Format
(1)  (2)  (3)  (4)  (5)  (6)  (7)  (8)  (9)  (10) 

/EBCS/PRES/ebcs_ID/unit_ID  
ebcs_title  
surf_ID  
C  
fct_ID_{pr}  Fscale_{pr}  
fct_ID_{rho}  Fscale_{rho}  
fct_ID_{en}  Fscale_{en}  
l_{c}  r_{1}  r_{2} 
Definition
Field  Contents  SI Unit Example 

ebcs_ID  Elementary boundary
condition identifier. (Integer, maximum 10 digits) 

unit_ID  Unit Identifier (Integer, maximum 10 digits) 

ebcs_title  Elementary boundary
condition title. (Character, maximum 100 characters) 

surf_ID  Surface
identifier. (Integer) 

C  Speed of sound. Default = 0 (Real) 
$\left[\frac{\text{m}}{\text{s}}\right]$ 
fct_ID_{pr}  Function
${\mathrm{f}}_{pr}\left(t\right)$
identifier for pressure.
(Integer) 

Fscale_{pr}  Pressure scale
factor. Default = 0 (Real) 
$\left[\text{Pa}\right]$ 
fct_ID_{rho}  Function
${\mathrm{f}}_{rho}\left(t\right)$
identifier for density.
(Integer) 

Fscale_{rho}  Density scale
factor. Default = 0 (Real) 
$[\frac{\text{kg}}{{\text{m}}^{3}}]$ 
fct_ID_{en}  Function
${\mathrm{f}}_{en}\left(t\right)$
identifier for energy.
(Integer) 

Fscale_{en}  Energy scale
factor. Default = 0 (Real) 
$\left[\text{J}\right]$ 
${l}_{c}$  Characteristic
length. Default = 0 (Real) 
$\left[\text{m}\right]$ 
r_{1}  Linear resistance. 5 Default = 0 (Real) 
$\left[\frac{\text{kg}}{{\text{m}}^{2}\text{s}}\right]$ 
r_{2}  Quadratic resistance.
5 Default = 0 (Real) 
$\left[\frac{\text{kg}}{{\text{m}}^{3}}\right]$ 
Comments
 Input is general, no prior assumptions are enforced! Verify that the elementary boundaries are consistent with general assumptions of ALE (equation closure).
 It is not advised to use the Hydrodynamic Bimaterial Liquid Gas Law (/MAT/LAW37 (BIPHAS)) with the elementary boundary conditions.
 Density, pressure, and energy are imposed according to a scale factor and a time function. If the function number is 0, the imposed density, pressure and energy are used.
 This keyword is less than four
or equal to six (nonreflective frontiers (NRF)) using:
(1) $$\frac{\partial P}{\partial t}=\rho c\frac{\partial {V}_{n}}{\partial t}+c\frac{\left({P}_{\infty}P\right)}{{l}_{c}}$$Pressure in the far field ${P}_{\infty}$ is imposed with a function of time. The transient pressure is derived from ${P}_{\infty}$ , the local velocity field V and the normal of the outlet facet.
Where, ${l}_{c}$ is the characteristic length, to compute cutoff frequency ${f}_{c}$ as:(2) $${f}_{c}=\frac{c}{2\pi .{l}_{c}}$$  A resistance pressure is
computed and added to the current pressure.
(3) $${P}_{res}={r}_{1}\cdot {V}_{n}+{r}_{2}\cdot {V}_{n}\cdot \left{V}_{n}\right$$It aims at modeling the friction loss due to the valves.