/EBCS

Block Format Keyword Describes the elementary boundary condition sets.

Format

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
/EBCS/`type`/`ebcs_ID`/`unit_ID`
`ebcs_title`

Type: GRADP0, PRES, VALVIN or VALVOUT

(1)	(2)	(3)	(5)
`surf_ID`
`C`
`fct_ID`_pr	`Fscale`_pr
`fct_ID`_rho	`Fscale`_rho
`fct_ID`_en	`Fscale`_en
`l`_c		`r`₁	`r`₂

Type: VEL

(1)	(2)	(3)	(5)
`surf_ID`
`C`
`fct_ID`_vx	`Fscale`_vx
`fct_ID`_vy	`Fscale`_vy
`fct_ID`_vz	`Fscale`_vz
`fct_ID`_rho	`Fscale`_rho
`fct_ID`_en	`Fscale`_en
`l`_c		`r`₁	`r`₂

Type: NORMV

(1)	(2)	(3)	(5)
`surf_ID`
`C`
`fct_ID`_vim	`Fscale`_vim
`fct_ID`_rho	`Fscale`_rho
`fct_ID`_en	`Fscale`_en
`l`_c		`r`₁	`r`₂

Type: INIP, INIV

(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)	(9)	(10)
`surf_ID`
`Rho`		`C`		$l_{c}$ $l_{c}$

Definitions

Field	Contents	SI Unit Example
`type`	Elementary boundary condition keyword. (see EBCS Type for available keywords)
`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)	$[\frac{m}{s}]$ $[\frac{m}{s}]$
`fct_ID`_pr	Function $f_{p r} (t)$ $f_{p r} (t)$ identifier for pressure. = 0 $P = F s c a l e_{p r}$ $P = F s c a l e_{p r}$ = n $P = F s c a l e_{p r} \cdot f_{p r} (t)$ $P = F s c a l e_{p r} \cdot f_{p r} (t)$ (Integer)
`Fscale`_pr	Pressure scale factor. Default = 0 (Real)	$[Pa]$ $[Pa]$
`fct_ID`_rho	Function $f_{r h o} (t)$ $f_{r h o} (t)$ identifier for density. = 0 $ρ = F s c a l e_{r h o}$ $ρ = F s c a l e_{r h o}$ = n $ρ = F s c a l e_{r h o} \cdot f_{r h o} (t)$ $ρ = F s c a l e_{r h o} \cdot f_{r h o} (t)$ (Integer)
`Fscale`_rho	Density scale factor. Default = 0 (Real)	$[\frac{kg}{m^{3}}]$ $[\frac{kg}{m^{3}}]$
`fct_ID`_en	Function $f_{e n} (t)$ $f_{e n} (t)$ identifier for energy. = 0 $E = F s c a l e_{e n}$ $E = F s c a l e_{e n}$ = n $E = F s c a l e_{e n} \cdot f_{e n} (t)$ $E = F s c a l e_{e n} \cdot f_{e n} (t)$ (Integer)
`Fscale`_en	Energy scale factor. Default = 0 (Real)	$[J]$ $[J]$
$l_{c}$ $l_{c}$	Characteristic length. Default = 0 (Real)	$[m]$ $[m]$
`r`₁	Linear resistance. 6 Default = 0 (Real)	$[\frac{kg}{m^{2} s}]$ $[\frac{kg}{m^{2} s}]$
`r`₂	Quadratic resistance. 6 Default = 0 (Real)	$[\frac{kg}{m^{3}}]$ $[\frac{kg}{m^{3}}]$
`fct_ID`_vx	Function $f_{V X} (t)$ $f_{V X} (t)$ identifier for X velocity. = 0 $V_{X} = F s c a l e_{V X}$ $V_{X} = F s c a l e_{V X}$ = n $V_{X} = F s c a l e_{V X} \cdot f_{V X} (t)$ $V_{X} = F s c a l e_{V X} \cdot f_{V X} (t)$ (Integer)
`Fscale`_vx	X velocity scale factor. Default = 0 (Real)	$[\frac{kg}{m^{3}}]$ $[\frac{kg}{m^{3}}]$
`fct_ID`_vy	Function $f_{V Y} (t)$ $f_{V Y} (t)$ identifier for Y velocity. = 0 $V_{Y} = F s c a l e_{V Y}$ $V_{Y} = F s c a l e_{V Y}$ = n $V_{Y} = F s c a l e_{V Y} \cdot f_{V Y} (t)$ $V_{Y} = F s c a l e_{V Y} \cdot f_{V Y} (t)$ (Integer)
`Fscale`_vy	Y velocity scale factor. Default = 0 (Real)	$[\frac{m}{s}]$ $[\frac{m}{s}]$
`fct_ID`_vz	Function $f_{V Z} (t)$ $f_{V Z} (t)$ identifier for Z velocity. = 0 $V_{Z} = F s c a l e_{V Z}$ $V_{Z} = F s c a l e_{V Z}$ = n $V_{Z} = F s c a l e_{V Z} \cdot f_{V Z} (t)$ $V_{Z} = F s c a l e_{V Z} \cdot f_{V Z} (t)$ (Integer)
`Fscale`_vz	Z velocity scale factor. Default = 0 (Real)	$[\frac{m}{s}]$ $[\frac{m}{s}]$
`fct_ID`_vim	Function $f_{v i m} (t)$ $f_{v i m} (t)$ identifier for imposed velocity. = 0 $V = F s c a l e_{v i m}$ $V = F s c a l e_{v i m}$ = n $V = F s c a l e_{v i m} \cdot f_{v i m} (t)$ $V = F s c a l e_{v i m} \cdot f_{v i m} (t)$ (Integer)
`Fscale`_vim	Imposed velocity. Default = 0 (Real)	$[\frac{m}{s}]$ $[\frac{m}{s}]$
`Rho`	Initial density. Default = 0 (Real)	$[\frac{kg}{m^{3}}]$ $[\frac{kg}{m^{3}}]$

EBCS Type

Table 1. Element Compatibilities with Material
Type	Keyword	Description
0	`GRADP0`	Zero pressure gradient. Is not allowed for SPMD parallel version.
1	`PRES`	Imposed density and pressure
2	`VALVIN`	Inlet valve (Imposed density and pressure)
3	`VALVOUT`	Outlet valve (Imposed density and pressure)
4	`VEL`	Imposed velocity
5	`NORMV`	Imposed normal velocity
6	`INIP`	Initial pressure
7	`INIV`	Initial velocity

Comments

Input is general, no prior assumptions are enforced! You must verify that the elementary boundaries are consistent with general assumptions of ALE (equation closure).
It is not advised to use the Hydrodynamic Bi-material Liquid Gas Law (/MAT/LAW37 (BIPHAS)) with the elementary boundary conditions.
Density, pressure, 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.
All EBCS which type is less tha four or equal to six are non-reflective frontiers (NRF), using:
(1)
$\frac{\partial P}{\partial t} = ρ c \frac{\partial V_{n}}{\partial t} + c \frac{(P_{\infty} - P)}{l_{c}}$ $\frac{\partial P}{\partial t} = ρ c \frac{\partial V_{n}}{\partial t} + c \frac{(P_{\infty} - P)}{l_{c}}$

Pressure in the far field $P_{\infty}$ $P_{\infty}$ is imposed with a function of time. The transient pressure is derived from $P_{\infty}$ $P_{\infty}$ , the local velocity field V and the normal of the outlet facet.

Where, $l_{c}$ $l_{c}$ is the characteristic length, to compute cutoff frequency $f_{c}$ $f_{c}$ as:(2)
$f_{c} = \frac{c}{2 π . l_{c}}$ $f_{c} = \frac{c}{2 π . l_{c}}$
In order to impose a positive velocity fct_ID_vim (for instance 15 m/s), you must input -fct_ID_vim (for instance -15 m/s).
A resistance pressure is computed and added to the current pressure.(3)
$P_{r e s} = r_{1} \cdot V_{n} + r_{2} \cdot V_{n} \cdot | V_{n} |$ $P_{r e s} = r_{1} \cdot V_{n} + r_{2} \cdot V_{n} \cdot | V_{n} |$

It aims at modeling the friction loss due to the valves.