# /EBCS/INIP

Block Format Keyword Describes the elementary boundary condition of initial pressure.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/EBCS/INIP/ebcs_ID/unit_ID
ebcs_title
surf_ID
Rho C ${l}_{c}$

## 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)

Rho Initial density.

Default = 0 (Real)

$\left[\frac{\text{kg}}{{\text{m}}^{\text{3}}}\right]$
C Speed of sound.

Default = 0 (Real)

$\left[\frac{\text{m}}{\text{s}}\right]$
${l}_{c}$ Characteristic length.

Default = 0 (Real)

$\left[\text{m}\right]$

1. Input is general, no prior assumptions are enforced! Verify that the elementary boundaries are consistent with general assumptions of ALE (equation closure).
2. It is not advised to use the Hydrodynamic Bi-material Liquid Gas Law (/MAT/LAW37 (BIPHAS)) with the elementary boundary conditions.
3. 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.
4. This keyword is less than four or equal to six (non-reflective frontiers (NRF)) using:

$\frac{\partial P}{\partial t}=\rho c\frac{\partial {V}_{n}}{\partial t}+c\frac{\left({P}_{\infty }-P\right)}{{l}_{c}}$

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:

${f}_{c}=\frac{c}{2\pi .{l}_{c}}$

5. A resistance pressure is computed and added to the current pressure.
${P}_{res}={r}_{1}\cdot {V}_{n}+{r}_{2}\cdot {V}_{n}\cdot |{V}_{n}|$

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