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RADIOSS Application in Airbag Simulation

作者:Simwe    来源:Altair    发布时间:2013-06-21    收藏】 【打印】  复制连接  【 】 我来说两句:(0逛逛论坛

RADIOSS Application in Airbag Simulation

Haibin OuYang, Peigang Su, Shuibo Wu

(YanFeng KSS (Shanghai) Automotive Safety Systems CO.,Ltd 201315)

Abstract: Virtual modeling and simulation are increasingly used to help develop restraint systems, and airbag simulation is the necessary steps during airbag research and design progress. This paper introduces RADIOSS application in airbag simulation. The dynamic simulation has been checked with physical test and shows very good correlation, which proves that airbag modeling is reliable and acceptable.

Keywords: Tank Test, Airbag Validation, Drop Tower, RADIOSS

1 Introduction

Virtual modeling and simulation are increasingly used to help develop restraint systems and enhance the value of virtual design with simulation are regularly used by system supplier,which is effective in evaluating and optimizing the performance of restraint systems[1].

The most common airbag simulation method assumes uniform pressure and temperature everywhere inside the airbag. This is a close representative of the airbag after it is fully inflated and the gas flow inside airbag stabilizes. This paper uses uniform pressure method to achieve airbag validation.

2 Theory

An airbag model in RADIOSS is defined as a monitor volume, the most important parts of airbag definition are gas properties of mass injection and outgoing mass, the latter often includes vent hole outgoing flow and porosity outgoing flow due to fabric material property.

2.1 Mass injection[3]

The amount of mass injected into the airbag needs to be defined with respect to time. The data can be obtained by airbag manufacturer or a tank experiment. A diagram of a classic tank experiment can be seen in Figure 1.

The mass versus time curve can be derived from the pressure curve if  is known:

(1)

Where, M is the molecular weight of the injected gas, R is the perfect gas constant :

The average estimate for temperature of injection is:

 (2)

Where,  is the total pressure variation during the experiment.  is the total injected mass, which can be derived from the mass of propellant in the pyrotechnic inflator and the chemical reaction.

2.2 Outgoing mass determination[3]

2.2.1 Isenthalpic model

Venting or the expulsion of gas from the volume, the status 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.
Conservation of enthalpy leads to velocity  at the vent hole.  The Bernouilli Equation is then written as:

 (3)

Applying the adiabatic conditions:

 (4)

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

Therefore, the exit velocity is given by:

 (5)

Whereis the averaged density of the gas andis the fraction of massic averages of heat capacities at constant pressure and constant volume.

The mass out flow rate is given by:

 (6)

2.2.2 Chemkin model

Porosity definition can define the surface for outgoing flow with the following equation:

 (7)

Where  is the density of the gas within the airbag,  is the outflow velocity function defined by users.

 
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