Multi-compartment Side Curtain Airbag Deployment

Chapter 22: Multi-Compartment Side Curtain Airbag Deployment

22

Multi-compartment Side Curtain Airbag Deployment 

Summary



Introduction



Requested Solutions



Airbag Analysis Scheme



FEM Solution



Results



Input File(s)

420 421

421

423 424

421 421

420 MD Demonstration Problems CHAPTER 22

Summary Title

Chapter 22: Multi-compartment Side Curtain Airbag Deployment

Features

Deploy Multi-compartment Side Curtain Airbag

Geometry

Fix

Gas supply bag

Compartment

Inflator

= gth Len

2m 0.75

Material properties

See Summary of Materials.

Analysis type

Transient explicit dynamic analysis

Boundary conditions

Fixed at brackets

Applied loads

Prescribed pressure and temperature of inflator gas

Element type

Airbag: 2-D triangular shell element Airbag gas: 3-D solid element (automatically generated)

FE results

60 m t = 0.3 Heigh

CHAPTER 22 421 Multi-compartment Side Curtain Airbag Deployment

Introduction .The purpose of this example is to demonstrate the simulation of a multi-compartment airbag; a capability is introduced in MD Nastran SOL 700 (SOL 700). AIRBAG, GRIA, and EOSGAM are added in Bulk Data entries to support the capability.

Requested Solutions The airbag has five compartments. These compartments are folded, and each compartment is connected to the gas supply bag through a large hole. An inflator is modeled next to the gas supply bag. The gas jet is initiated from the inflator and running into the gas supply bag. Fixed boundary conditions are applied to the brackets attached to the gas supply bag. The simulation time is 0.04 seconds.

Airbag Analysis Scheme MD Nastran SOL 700 Airbag Model (bdf)

SOL 700

Obtain Binary Results -

Deformation (AIRBAG)

-

CFD result (GAS)

FEM Solution The units of this model are kg for weight, meter for length, second for time, and Kelvin for temperature. TSTEPNL describes the number of Time Steps (100) and Time Increment (0.0004 seconds) of the simulation. End time

is the product of the two entries. Notice here, the Time Increment is only for the first step. The actual number of Time Increments and the exact value of the Time Steps are determined by SOL 700 during the analysis. The step size of the output files is determined by the Time Increment as well. TSTEPNL

1

100

.0004

1

ADAPT

2

10

422 MD Demonstration Problems CHAPTER 22

One inflator and five compartment AIRBAG entries are defined. An AIRBAG entry instructs SOL 700 to create an airbag using either the CFD method (full gas dynamics) or using a uniform gasbag method. Here, the full gas dynamic method is used for all airbag definitions. Inflow of gas into the airbag is defined by the entries following the INFLATOR key word. Outflow is defined by adding LARGHOLE to the inflator which is connected to the five different compartment airbag. Details of an AIRBAG entry are described below: Airbag 1 is the definition of the inflator airbag. The CFD option defines CFD related data. Gamma law equation of state is defined referring the EOSGAM 3 field. AIRBAG +

1 CFD

25 3

1.527

0.009

0.009

0.009

+ +

Using the INITIAL option, initial conditions of gas property inside an airbag are defined. Initial pressure is 101,325 N/m2, initial temperature is 293 K, initial gamma gas constant is 1.4 and initial R gas constant is 294 N·m2/s2/K. +

INITIAL 101325. 293.

1.4

294.

+

The INFLATOR option is used to define gas property from an inflator. Mass flow rate is defined referring a table data (TABLED1). Temperature of inflowing gas is 350 K, a scale factor of available inflow area is 0.7, the gamma gas constant of the inflator gas is 1.557, and the R gas constant of the inflator gas is 243 N·m2/s2/K. + +

INFLATOR1001 1.557

1 243.

350.

0.7

+ +

The LARGEHOLE option defines the compartment location where gas flows into. In the example below, the first field, LARGHOLE 301 indicates that gas flows through surface 301 into the compartment with ID 2. A scale factor of inflow area is 1.0, meaning that 100% of the gas flows in. Five LARGEHOLE‘s definitions are used to model the gas flow inside the five airbag compartments. + + + + +

LARGHOLE301 LARGHOLE302 LARGHOLE303 LARGHOLE304 LARGHOLE305

2 3 4 5 6

1.0 1.0 1.0 1.0 1.0

+ + + +

AIRBAG entries from 2 to 6 define the compartments in the airbag.

AIRBAG + +

2 35 CFD 3 INITIAL 101325. 293.

1.527 1.4

0.011 294.

0.011

0.011

+ +

EOSGAM defines the ideal gas inside the airbag. This entry is used for each airbag definition. The gamma law gas equation of state is defined by EOSGAM. The pressure p is defined as:  =   – 1   e

where  is a constant, e is specific internal energy per unit mass,  is overall material density. A  constant of 1.517 and R gas constant of 226.4 m2/s2/K are used in this model.

CHAPTER 22 423 Multi-compartment Side Curtain Airbag Deployment

EOSGAM

3

1.517

226.4

The GRIA entry defines the final unstretched configuration of a deployed bag. All ID’s of GRIA entries must be the same as the ID’s of GRID entries. GRIA ...

1

.0009375-.626128 .230000

Summary of Materials Inflator airbag: fabric material (MATD034):  density=

783 kg/m3

Ea

(Young’s Modulus - longitudinal direction) = 2.6e+08

Eb

(Young’s Modulus - transverse direction) = 2.6e+08

a

(Poisson’s ratio - longitudinal direction) = .3

b

(Poisson’s ratio – transverse direction) = .3

Compartment airbag: null material (MATD009):  density=

783 kg/m3

E

(Young’s Modulus) = 2.6e+08



(Poisson’s ratio) = .3

Initial condition of airbag gas:  density)

= 1.527 kg/m3

Initial temperature = 293 K Initial pressure = 101,325 N/m2 Initial gamma gas constant = 1.4 Initial R gas constant = 294 N·m2/s2/K

Results There are two types of results files: ARC and d3plot. The ARC file is the original MSC.Dytran binary result file and includes the results for the Euler elements (fluid). d3plot is the native LS-DYNA result file format.

424 MD Demonstration Problems CHAPTER 22

t=0

t=2

t=4

t=6

t=8

t = 10

t = 20

t = 30 Airbag Deformed Shape

Time (ms)

t = 40

Figure 22-1

Euler Adaptive Mesh

Deformed Shape Airbag and Adaptive Euler Mesh

Input File(s) File nug_22.dat

Description MD Nastran input file for multi-compartment airbag FSI example