Moji Moatamedi

Multiphysics out of position airbag simulation

The deployment of an airbag is most fatal and dangerous to a passenger when it is in an out of position (OOP) situation, with the airbag making contact before it is fully inflated. This can lead to severe, if not life threatening, injuries to the passenger. This situation is more commonly associated with small females and children who are positioned near to the airbag module, i.e. in an OOP load case. The aim of this research is to assess the response of a Hybrid III 5th percentile female anthropomorphic dummy positioned in an FMVSS 208 low risk static airbag deployment OOP load cases using a transient dynamic finite element program called LS-DYNA. The simulation considers the standard procedures utilised in the LS-DYNA, where assumptions such as uniform airbag pressure and temperature are made, along with a more recently developed procedure that takes into account the fluid-structure interaction between the inflating gas source and the airbag fabric, referred to as arbitrary Lagrangian Eulerian (ALE) theory. Both simulations were compared to test data received by Jaguar, indicating satisfactory results in terms of correlation, with the more recently developed procedure, ALE theory, showing the greatest accuracy, both in terms of graphical and schematic comparison, especially in the very early stages of the inflation process. As a result, the new simulation procedure model was utilised to research into the effects of changing the designs of the airbag module.

A finite element model to identify electrode influence on current distribution in the skin

Discomfort experienced during surface functional electrical stimulation (FES) is thought to be partly a result of localized high current density in the skin underneath the stimulating electrode. This article describes a finite element (FE) model to predict skin current density distribution in the region of the electrode during stimulation and its application to the identification of electrode properties that may act to reduce sensation. The FE model results show that the peak current density was located in an area immediately under the stratum corneum, adjacent to a sweat duct. A simulation of surface FES via a high-resistivity electrode showed a reduction in this peak current density, when compared to that with a low-resistivity electrode.

A review of airbag test and analysis

In recent years there have been many airbag-related injuries and fatalities. These have been due to the airbag interacting with the occupant during out-of-position (OOP) states. Numerical simulation of this situation is currently under investigation. This article reviews the mathematical models that have been developed and utilised for in-position (IP) occupant analysis, showing their capabilities in crash simulations and their inefficiency for OOP occupant interaction. The review then describes a new simulation technique, fluid structure interaction, which can possibly model the OOP occupant interaction. The capabilities of this new method are described and how it can be utilised for this type of simulation, along with recommendations of future work in this area.

A new analytical model for high-velocity impact of thick composites

Abstract A new analytical impact/penetration model has been developed for high-velocity impact of thick composite targets using a spring-mass equivalent energy dissipating finite element/finite difference scheme. The initial basic model includes energy dissipating mechanisms such as punching shear and fiber breakage. The impact/penetration law, which is based on a linear distribution of punching shear force, is represented by a stiffness parameter. The equivalent variable mass of the composite target is built into the model by considering two-dimensional shear wave propagation, and its effective stiffness was initially represented by a nonlinear spring stiffness that is obtained from analyzing an infinite hollow cylinder subjected to internal in-plane shear. The two stiffness parameters are characterized by analyzing the forces between the impactor and the composite target at increasing depths of penetration through a series of quasi-static finite element analyses. Results are used to provide a more accurate prediction if the impactor would perforate or stop, and to obtain an estimate of its exit velocity or the depth of penetration for both blunt-ended and sharp-ended impactors penetrating a thick composite target at high speed. Analyses were performed to demonstrate different high-velocity impact scenarios.

Application of the penalty coupling method for the analysis of blood vessels

Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory.

Initialisation of volume fraction in fluid/structure interaction problem

Abstract In this paper, an algorithm that generates volume fraction initialisation for fluid-structure interaction problems is presented and implemented in an Arbitrary Lagrangian Eulerian (ALE) code. This algorithm improves the flexibility and efficiency of multi-material ALE formulations, enabling fluid-structure coupling problems to be dealt with, in which complex-shaped structures are embedded in a Cartesian fluid mesh, and where several fluid materials are involved. When implemented in a finite element code the algorithm will be extremely useful in the modelling of highly transient problems involving fluid-structure interactions and complex structural topologies. In such problems the volume fraction of each cell must be accurately initialised in order for the fluid-structure coupling algorithm to be effective. In many fluid-structure coupling problems if the volume fraction initialisation is not processed properly, the coupling algorithm leads to numerical fluid leakage through the structure involving an erroneous solution. In this paper the volume fraction initialisation method is described in detail and applied to the modelling of a cylindrical shock tube problem and to a crash problem involving a fuel tank of complex geometry under braking conditions.

Experimental and Numerical Simulation of Structure/Water Impact

This paper describes the numerical modeling of the impact of a rigid hemispherical structure upon water, using LS–DYNA [1] explicit dynamics software, and the validation of the modeling by comparison with theory and experiment. Firstly a theoretical solution, based upon conservation of momentum, is presented for the acceleration of a rigid spherically based capsule during vertical impact upon water. Next the design of a vertical water impact test rig is described and preliminary results for a 3.6m/s impact are presented. Finally the numerical analysis methodology used in LS DYNA is explained and then applied to simulate the 3.6m/s vertical impact experiment. The simulation results are compared to the experiment and theory, showing reasonable agreement. The discrepancies in the results are discussed in detail and further work in this area is suggested.Copyright

Study and Analysis of the Fluid-Structure Interaction Between Apple and Underwater Shock Wave

Shock wave treatment of an apple can produce a soft apple similar to a sponge containing water. Therefore, without needing to cut and grate apples, apple juice can be easily obtained by squeezing by hand. In a previous result, it was reported that more than 40MPa shock pressure was needed to make a soft apple. From observation for the shock treatment for the apple, an oblique wave was produced from a detonating fuse and the wave reflected at the surface of the apple. The resulting shock wave data was obtained. In the result of further observations, there was the possibility that the wave passing through the apple was attenuated faster than the wave passing through water. In this report, the same method in the previous research was used. Apples, detonating fuse, and electric detonator were set in water tank, with the fuse initiated by electric detonator. In this research, the behavior of shock wave passing through an apple was researched as exploratory experiment for numerical analysis. In the future, we want to attempt to analyze the fluid-structure interaction between the apple and underwater shock wave by using computer finite element analysis.Copyright

A New Fluid Structure Coupling Method for Airbag OOP

The deployment of an airbag is most fatal and dangerous to a passenger when they are in an out of position (OOP) situation, with the airbag making contact before it is fully inflated. This can lead to severe, if not life threatening, injuries to the passenger. This situation is more commonly associated with small females and children who are positioned near to the airbag module, i.e. in an OOP load cases. The aim of this research is to assess the response of a Hybrid III 5 Percentile female anthropomorphic dummy positioned in a FMVSS 208 low risk static airbag deployment OOP load cases using a transient dynamic finite element program called LS-DYNA. The simulation considers the standard procedures utilised in the LSDYNA, where assumptions such as uniform airbag pressure and temperature are made, along with a more recently developed procedure that takes into account the fluid-structure interaction between the inflating gas source and the airbag fabric, referred to as Arbitrary Lagrangain Eulerian (ALE) theory. Both simulations were compared to test data received by Jaguar, indicating satisfactory results in terms of correlation, with the more recently developed procedure, ALE theory, showing the greatest accuracy, both in terms of graphical and schematic comparison, especially in the very early stages of the inflation process. As a result, the new simulation procedure model was utilised to research into the effects of changing the designs of the airbag module. 102 M. Moatamedi et al.

Numerical and Experimental Study of Destruction of Metal Pipes Through Use of High Explosive

Various liquids are commonly transported through metal pipes. For reasons of safety it is important to understand the behavior of pipes when subject to an explosive loading from within. This research paper is concerned with examining the expansion and destruction of metal pipes subjected to a high power explosion by high explosive. An experimental study was carried out for this research and visualized using high-speed camera images. Results were then compared to a computer simulation of the same problem. Numerical simulations are performed in three dimensions using the LS-DYNA code. Results obtained numerically compared well to those from experiment.Copyright