/MONVOL/AIRBAG (Obsolete)

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
				Pext		T0		Iequi	Ittf
i		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_IDP	fct_IDP		Fscalept		Fscalep		Fscalep

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)

(1)	(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'

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)
AscaleP	Abscissa scale factor for pressure based functions Default = 1.0 (Real)
AscaleS	Abscissa scale factor for area based functions Default = 1.0 (Real)
AscaleA	Abscissa scale factor for angle based functions Default = 1.0 (Real)
AscaleD	Abscissa scale factor for distance based functions Default = 1.0 (Real)
mat_ID	Initial gas material identifier (see /MAT/GAS) (Real)
	Volumetric viscosity Default = 0.01 (Real)
Pext	External pressure (Real)
T0	Initial temperature Default = 295 (Real)
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.
i	Ratio of specific heats at initial temperature (Real)
cpai	cpa coefficient in the relation cpi(T) (Real)
cpbi	cpb coefficient in the relation cpi(T) (Real)
cpci	cpc coefficient in the relation cpi(T) (Real)
Njet	Number of injectors (Integer)
	Ratio of specific heats (Real)
cpa	cpa coefficient in the relation cp(T) (Real)
cpb	cpa coefficient in the relation cp(T) (Real)
cpc	cpa coefficient in the relation cp(T) (Real)
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)	, 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)	, if surf_IDV = 0
Tstop	Stop time for venting Default = 1E+30 (Real)
Tvent	Start time for venting Default = 0.0 (Real)
	Pressure difference to open vent hole membrane () (Real)
	Minimum duration pressure exceeds Pdef to open vent hole membrane (Real)
fct_IDV	Outflow velocity function identifier (Integer)
FscaleV	Scale factor on fct_IDV Default = 1.0 (Real)
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)	or
fct_IDT	Temperature of injected gas vs time function identifier (Integer)
FscaleT	Temperature function scale factor Default = 1.0 (Real)
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 P(t) (Integer)
fct_IDP	If Ijet = 1: identifier of the function number defining P() (Integer)
fct_IDP	If Ijet = 1: identifier of the function number defining P() (Integer)
FscalePt	If Ijet = 1: scale factor for fct_IDPt Default = 1.0 (Real)
FscaleP	If Ijet = 1: scale factor for fct_IDP Default = 1.0 (Real)
FscaleP	If Ijet = 1: scale factor for fct_IDP Default = 1.0 (Real)
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)

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:

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.

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:

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 i 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:

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

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 i = 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 must be related to specific heat per mass unit at initial temperature and molar mass of the with respect to the following relation:

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

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

Pjet = P(t) * P() * P() * max ( * ,0)

13.

With

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

(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:

= 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

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:

and non-impacted surface:

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)

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 .

/MONVOL/AIRBAG (Obsolete)

/MONVOL/AIRBAG (Obsolete)

/MONVOL/AIRBAG (Obsolete)

Format

See Also: