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/MONVOL/AIRBAG (Obsolete)

/MONVOL/AIRBAG (Obsolete)

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/MONVOL/AIRBAG (Obsolete)

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Block Format Keyword

/MONVOL/AIRBAG - Airbag

Description

Describes the airbag monitored volume type.

Format

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

/MONVOL/AIRBAG/monvol_ID/unit_ID

monvol_title

surf_IDex

 

 

 

 

 

 

 

 

 

Ascalet

AscaleP

AscaleS

AscaleA

AscaleD

 

 

symbol_u

Pext

T0

Iequi

Ittf

yi

cpai

cpbi

cpci

 

 

 

Number of Injectors

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

Njet

 

 

 

 

 

 

 

 

 

 

Define Njet injectors (3 Lines per injector)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

cpa

cpb

cpc

 

 

fct_IDmas

Iflow

Fscalemas

fct_IDT

FscaleT

sens_ID

 

 

Ijet

node_ID1

node_ID2

node_ID3

 

 

 

 

 

 

 

Jetting Functions data (Read only if Ijet > 0)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

fct_IDPt

fct_IDPclip0556

fct_IDPsymbol_s

 

Fscalept

Fscalepclip0556

Fscalepsymbol_s

 

Number of vent holes

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

Nvent

 

 

 

 

 

 

 

 

 

 

Define Nvent vent holes membranes (four lines per vent hole membrane)

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(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

surf_IDv

Avent

Bvent

Tstop

 

 

 

Tvent

fct_IDV

FscaleV

IdtPdef

fct_IDt

fct_IDP

fct_IDA

 

Fscalet

FscaleP

FscaleA

fct_IDt’

fct_IDP

fct_IDA'

 

Fscalet'

FscaleP'

FscaleA'


hmtoggle_plus1Flag Definition

Field

Contents

SI Unit Example

monvol_ID

Monitored volume identifier

(Integer, maximum 10 digits)

 

unit_ID

Optional unit identifier

(Integer, maximum 10 digits)

 

monvol_title

Monitored volume title

(Character, maximum 100 characters)

 

surf_IDex

External surface identifier (see Comment 1)

(Integer)

 

Ascalet

Abscissa scale factor for time based functions

Default = 1.0  (Real)

symbol_S_unit

AscaleP

Abscissa scale factor for pressure based functions

Default = 1.0 (Real)

symbol_Pa

AscaleS

Abscissa scale factor for area based functions

Default = 1.0  (Real)

symbol_m_2

AscaleA

Abscissa scale factor for angle based functions

Default = 1.0 (Real)

symbol_deg

AscaleD

Abscissa scale factor for distance based functions

Default = 1.0 (Real)

symbol_m

mat_ID

Initial gas material identifier (see /MAT/GAS)

(Real)

 

symbol_u

Volumetric viscosity

Default = 0.01  (Real)

 

Pext

External pressure

(Real)

symbol_Pa

T0

Initial temperature

Default = 295  (Real)

fail_tab_temp

Iequi

Initial thermodynamic equilibrium flag

(Integer)

= 0: the mass of gas initially filling the airbag is determined with respect to the volume at time zero.

= 1: the mass of gas initially filling the airbag is determined with respect to the volume at beginning of jetting.

 

Ittf

Venting time shift flag. Active only when injection sensor is specified.

= 0 or 1: time dependent porosity curves are not shifted by injection sensor activation time. Tvent and Tstop are ignored.

= 2: time dependent porosity curves are shifted by Tinj (Tinj defined as the time of the first injector to be activated by the sensor). Tvent and Tstop are ignored.

= 3: time dependent porosity curves are shifted by Tinj +Tvent. Venting is stopped at Tinj + Tstop, when Tstop is specified.

 

yi

Ratio of specific heats at initial temperature

monvol_airbag3

(Real)

 

cpai

cpa coefficient in the relation cpi(T)

(Real)

symbol_heat

cpbi

cpb coefficient in the relation cpi(T)

(Real)

symbol_J_kg_K2

cpci

cpc coefficient in the relation cpi(T)

(Real)

symbol_J_kg_K3

Njet

Number of injectors

(Integer)

 

Ratio of specific heats

monvol_airbag4

(Real)

 

cpa

cpa coefficient in the relation cp(T)

(Real)

symbol_heat

cpb

cpa coefficient in the relation cp(T)

(Real)

symbol_J_kg_K2

cpc

cpa coefficient in the relation cp(T)

(Real)

symbol_J_kg_K3

surf_IDv

Vent holes membrane surface identifier

(Integer)

 

Avent

if surf_IDv 0: scale factor on surface
Default = 1.0

 

if surf_IDv = 0: surface of vent holes
Default = 0.0

(Real)

symbol_m_2, if surf_IDV = 0

Bvent

if surf_IDv 0: scale factor on impacted surface
Default = 1.0

 

if surf_IDv = 0: Bvent is reset to 0
Default = 0.0

(Real)

symbol_m_2, if surf_IDV = 0

Tstop

Stop time for venting

Default = 1E+30 (Real)

symbol_S_unit

Tvent

Start time for venting

Default = 0.0 (Real)

symbol_S_unit

Pressure difference to open vent hole membrane
()

(Real)

symbol_Pa

Minimum duration pressure exceeds Pdef to open vent hole membrane

(Real)

symbol_S_unit

fct_IDV

Outflow velocity function identifier

(Integer)

 

FscaleV

Scale factor on fct_IDV

Default = 1.0  (Real)

fail_lad_SI_k

IdtPdef

Time delay flag when is reached:

= 0: pressure should be over during a cumulative time to activate venting

= 1: venting is activated after is reached

 

fct_IDt

Porosity vs time function identifier

(Integer)

 

fct_IDP

Porosity vs pressure function identifier

(Integer)

 

fct_IDA

Porosity vs area function identifier

(Integer)

 

Fscalet

Scale factor for fct_IDt

Default = 1.0 (Real)

 

FscaleP

Scale factor for fct_IDP

Default = 1.0 (Real)

 

FscaleA

Scale factor for fct_IDA

Default = 1.0 (Real)

 

fct_IDmas

Mass of injected gas vs time function identifier

(Integer)

 

Iflow

Mass vs time function input type flag

(Integer)

= 0: mass is input

= 1: mass flow is input

 

Fscalemas

Mass function scale factor

Default = 1.0  (Real)

symbol_kg_unit or symbol_kg_s

fct_IDT

Temperature of injected gas vs time function identifier

(Integer)

 

FscaleT

Temperature function scale factor

Default = 1.0  (Real)

fail_tab_temp

sens_ID

Sensor identifier

(Integer)

 

Ijet

Jetting flag

(Integer)

= 0: no jetting

= 1: jetting

 

node_ID1, node_ID2, node_ID3

Node identifiers N1, N2, and N3 for jet shape definition

(Integer)

 

fct_IDPt

If Ijet = 1: identifier of the function number defining symbol_triP(t)

(Integer)

 

fct_IDPclip0556

If Ijet = 1: identifier of the function number defining symbol_triP(clip0556)

(Integer)

 

fct_IDPsymbol_s

If Ijet = 1: identifier of the function number defining symbol_triP(symbol_s)

(Integer)

 

FscalePt

If Ijet = 1: scale factor for fct_IDPt

Default = 1.0  (Real)

symbol_Pa

FscalePclip0556

If Ijet = 1: scale factor for fct_IDPclip0556

Default = 1.0  (Real)

symbol_Pa

FscalePsymbol_s

If Ijet = 1: scale factor for fct_IDPsymbol_s

Default = 1.0  (Real)

symbol_Pa

Nvent

Number of vent holes

(Integer)

 

fct_IDt’

Porosity vs time when contact function identifier

(Integer)

 

fct_IDP’

Porosity vs pressure when contact function identifier

(Integer)

 

fct_IDA’

Porosity vs impacted surface function identifier

(Integer)

 

Fscalet'

Scale factor for fct_IDt'

Default = 1.0 (Real)

 

FscaleP'

Scale factor for fct_IDP'

Default = 1.0 (Real)

 

FscaleA'

Scale factor for fct_IDA'

Default = 1.0 (Real)

 

hmtoggle_plus1Comments
1.surf_IDex must be defined using segments associated with 4-nodes or 3-nodes shell elements (possibly void elements).
2.The volume must be closed and the normals must be oriented outwards.
3.Abscissa scale factors are used to transform abscissa units in airbag functions, for example:

monvol_equat

where, t is the time.

For example, if your input data is in [ms], but you need a data in [s], you could set Ascale to 0.001.

monvol_equat2

where, p is the pressure.

4.Initial pressure is set to Pext.
5.Initial thermodynamic equilibrium is written at time zero (Iequi =0) or at beginning of jetting (Iequi =1), based on the following equation with respect to the volume at time zero, or the volume at beginning of jetting:

starter_monvol_Iequi

where, M0 is the mass of gas initially filling the airbag, Mi is the molar mass of the gas initially filling the airbag, and R is the gas constant depending on the units system.

6.Ratio of specific heats at constant pressure per mass unit cpi of the gas initially filling the airbag is quadratic versus temperature:

cpi(T) = cpa + cpbi * T + cpci * T2

7.Gas constant at initial temperature yi must be related to specific heat per mass unit at initial temperature and molar mass of the gas initially filling the airbag with respect to the following relation:

clip0508

where, Mi is the molar mass of the gas initially filling the airbag, and R is the gas constant depending on the units system.

clip0509

8.The characteristics of the gas initially filling the airbag must be defined (no default) and must be equal for each communicating airbag.
9.If yi = 0, the characteristics of the gas initially filling the airbag are set to the characteristics of the gas provided by the first injector.
10.Ratio of specific heats at constant pressure per mass unit cpi of the gas is quadratic with regard to the temperature:

cp(T) = cpa + cpb * T + cpc * T2

11.Gas constant at initial temperature Y must be related to specific heat per mass unit at initial temperature and molar mass of the with respect to the following relation:

clip0511

where,  M is the molar mass of the gas, and R is the gas constant depending on the units system.

clip0509

12.If jetting is used, an additional symbol_triPjet pressure is applied to each element of the airbag:

symbol_triPjet = symbol_triP(t) * symbol_triP(clip0556) * symbol_triP(symbol_s) * max (n_arrow * m_arrow2,0)

13.With m_arrow2 being the normalized vector between the projection of the center of the element upon segment (node_ID1 and node_ID3) and the center of the element; the angle between vectors MN2 and m_arrow2 (in degrees), is the distance between the center of the element and its projection upon segment (node_ID1 and node_ID3 ).

The projection of a point upon segment (node_ID1 and node_ID3) is defined as the projection of the point in direction MN2 upon the line (node_ID1 and node_ID3) if it lies inside the segment (node_ID1 and node_ID3). If this is not the case, the projection of the point upon segment (node_ID1 andnode_ID3) is defined as the closest node node_ID1 or node_ID3 (see following figure: dihedral shape of the jet).

clip0087

with M between N1 and N3

14.If node_ID3 = 0, node_ID3 is set to node_ID1 and the dihedral shape is reduced to a conical shape.
15.If fct_IDV = 0: isenthalpic outflow is assumed, else Chemkin model is used and outflow velocity is:

ratio = FscaleV * fct_IDV (P - Pext )

Isenthalpic model

Venting or the expulsion of gas from the volume, is assumed to be isenthalpic.

The flow is also assumed to be unshocked, coming from a large reservoir and through a small orifice with effective surface area, A.

Conservation of enthalpy leads to velocity, u, at the vent hole. The Bernouilli equation is then written as:

(monitored volume) clip0513 (vent hole)

Applying the adiabatic conditions:

(monitored volume) clip0514 (vent hole)

Where, P is the pressure of gas into the airbag and is the density of gas into the airbag.

Therefore, the exit velocity is given by:

clip0515

For supersonic flows the outlet velocity is determined as described in 10.4.4.1 of the Theory Manual.

The mass out flow rate is given by:

clip0516

The energy flow rate is given by:

clip0517

Where, V is the airbag volume and E is the internal energy of gas into the airbag.

Chemkin model

monvol_chemkin_equ

Where, is the density of the gas within the airbag.

16.Vent holes surface is computed as follows:

vent_holes_surface = Avent * Anon_impacted * fct_IDt(Anon_impacted /A0) * fct_IDP (P - Pext )

+ Bvent * Aimpacted * fct_IDt’(Aimpacted /A0) * fct_IDP (P - Pext )

with impacted surface:

monvol_impacted-surf

and non-impacted surface:

monvol_nonimpacted

where for each element e of the vent holes surf_IDv, nc(e) means the number of impacted nodes among the n(e) nodes defining the element.

(see following figure: from nodes contact to impacted/non-impacted surface)

Image12

17.Functions fct_IDt' and fct_IDP' are assumed to be equal to 1, if they are not specified (null identifier).
18.Function fct_IDA is assumed as the fct_IDA'(A) = A, if it is not specified.
19.In order to use porosity during contact, flag IBAG must be set to 1 in the interfaces concerned (Line 3 of interface Type 5 and Type 7). If not, the nodes impacted into the interface are not considered as impacted nodes in the previous formula for Aimpacted and Anon_impacted.
20.When defining venting, there are some limitations concerning the definition of airbag surface and surface venting:
The airbag external surface should be built only from shells and 3-nodes shell elements.
The airbag external surface can not be defined with option /SURF/SEG (or with option /SURF/SURF if a sub-surface is defined with option /SURF/SEG).
Same restriction applies to vent hole surface.
Shells and 3-nodes shell elements included in vent hole surface have to also be included in external surface.
21.Vent hole membrane is deflated if T > Tvent or if the pressure exceeds Pdef during more than .

See Also:

Airbag modeling in User's Guide

AIRBAG type Monitored Volume in Theory Manual

Example 27 - Football Shots