Christophe Bastien

Effects of roof crush loading scenario upon body in white using topology optimisation

This paper investigates the effects of variations in modelling of roof crush loading scenarios upon topology and mass of a body in white (BIW) for a hybrid electric vehicle (HEV). These variations incorporated the proposed changes to the Federal Motor Vehicle Safety Standards (FMVSS) 216 standard. The base model used for the investigation in this paper was based upon a series of optimisation studies. The overall purpose was to minimise the BIW mass of an HEV subjected to multiple crash scenarios including high-speed front impact, offset deformable barrier (ODB), side impact, pole impact, high-speed rear impact and low-speed rear impact in addition to a roof crush scenario. For the purpose of achieving this goal, finite element (FE) topology optimisation was employed. Owing to the limitations of present-day FE optimisation software, all models utilised linear static load cases. In addition, all models made use of inertia relief (IR) boundary conditions. With the above approach, the BIW topology was investigated.

Influence of vehicle secondary impact following an emergency braking on an unbelted occupant's neck, head and thorax injuries

Passive safety has for many years reduced the number of fatalities on the roads. However, its effect on occupants’ safety has now stabilised, meaning that new active safety features are needed to reduce further the number of casualties. These active safety features, like autonomous emergency braking (AEB), aim to prevent vehicle collisions and reduce the vehicle kinetic energy on impact. A previous study has shown that unbelted occupants kinematics are affected by the pre-braking phase, suggesting that the occupants hand positions on the steering wheel, combined with a bracing behaviour, could cause the occupant to miss the deploying airbag in the case of a secondary rigid wall impact. This paper will investigate the variations of the secondary vehicle impact crash patterns by calculating crash pulses based on typical vehicle frontal accident scenarios and conclude on these effects on the human occupants neck, head and thorax injuries.

Computer simulation of real-world vehicle–pedestrian impacts

This paper describes a study carried out to develop and apply computer analysis tools to simulate real-world accidents between vehicles and pedestrians. The main focus has been the incorporation of realistic pedestrian pre-impact gait motion and to investigate the outcome of real-world impacts. A combination of multi-body, FACET and finite element based vehicle models in conjunction with validated human body models developed by MADYMO were used to simulate and analyse vehicle–pedestrian accident scenarios. European regulations and consumer tests for passenger cars now address vehicle front aggressiveness, and vehicle manufactures have effectively developed design solutions for meeting these requirements. Vehicle frontal geometry and pedestrian pre-impact characteristics play a major role in determining the post-impact kinematics and severity of injury sustained during pedestrian–vehicle contact stage. A unique aspect of this study has been the application of the Injury Severity Index method developed for automotive occupant injury assessment to pedestrians. The injury results from the simulations were measured and the severity assessed by applying a quantitative rating method.

Buckling considerations and cross-sectional geometry development for topology optimised body in white

This paper will investigate how current state-of-the-art structural optimisation algorithms, with an emphasis on topology optimisation, can be used to rapidly develop lightweight body in white (BIW) concept designs, based on a computer aided design envelope. The optimisation models included in the paper will primarily focus on crashworthiness and roof crush scenarios as specified in the Federal Motor Vehicle Safety Standards (FMVSS) 216 standard. This paper is a continuation of a previously published paper, which investigated the potential effects of recently proposed changes to FMVSS 216 upon BIW mass and architecture using topology optimisation. The paper will investigate the possibilities of including buckling considerations of roof members directly into current state-of-the-art topology optimisation algorithms. This paper will also demonstrate the potential for developing a detailed BIW design including cross-sectional properties based on a styling envelope.

Tyre model development using co-simulation technique for helicopter ground operation

This paper describes the development of a new aircraft tyre model applied using a co-simulation approach for the multibody dynamic simulation of helicopter ground vehicle dynamics. The new tyre model is presented using a point follower approach that makes a novel contribution to this area by uniquely combining elements of two existing tyre models used by the aircraft industry, namely the NASA R64 model developed by Smiley and Horne and the Engineering Sciences Data Unit (ESDU) Mitchell tyre model. Before the tyre model was used with a full helicopter model, a virtual tyre test rig was used to examine the tyre and to predict the tyre forces and moments for a range of tyre states. The paper concludes by describing the successful application of the new tyre model with a full helicopter model and the simulation of representative landing, take-off and runway taxiing manoeuvres. The predictive capability of the model is demonstrated to show the open-loop ground vehicle dynamics response of the helicopter and also the ground load predictive capability for the distribution of loads through the tyres, wheels and landing gears.

An evidence based method to calculate pedestrian crossing speeds in vehicle collisions (PCSC)

Pedestrian accident reconstruction is necessary to establish cause of death, i.e. establishing vehicle collision speed as well as circumstances leading to the pedestrian being impacted and determining culpability of those involved for subsequent court enquiry. Understanding the complexity of the pedestrian attitude during an accident investigation is necessary to ascertain the causes leading to the tragedy. A generic new method, named Pedestrian Crossing Speed Calculator (PCSC), based on vector algebra, is proposed to compute the pedestrian crossing speed at the moment of impact. PCSC uses vehicle damage and pedestrian anthropometric dimensions to establish a combination of head projection angles against the windscreen; this angle is then compared against the combined velocities angle created from the vehicle and the pedestrian crossing speed at the time of impact. This method has been verified using one accident fatality case in which the exact vehicle and pedestrian crossing speeds were known from Police forensic video analysis. PCSC was then applied on two other accident scenarios and correctly corroborated with the witness statements regarding the pedestrians crossing behaviours. The implications of PCSC could be significant once fully validated against further future accident data, as this method is reversible, allowing the computation of vehicle impact velocity from pedestrian crossing speed as well as verifying witness accounts.

Enhancing Noise Attenuation in Exhaust Mufflers on Response to Baffle Configuration

Using baffles in exhaust mufflers is known to improve transmission loss and reduce the noise emitted to the environment. This paper postulates that baffle cut ratio affects the muffler performance in the same effect as a shell-and-tube heat exchanger, consequently the baffle cut ratio should affect the muffler performance. This study presents a parametric study on the effect of baffle configuration on predicted transmission loss and pressure drop. The effect of baffle cut ratio, baffle spacing, number of baffle holes, and hole pattern distribution on transmission loss was investigated. Results showed that reducing the baffle cut ratio increased the transmission loss at intermediate frequencies by up to 45% while decreasing the spacing between muffler plates improved the muffler transmission loss by 40%. The assessment of the baffle effect on flow using a thermal baffle approach model indicated a sudden drop in fluid temperature in axial flow direction by 15% as the baffle cut ratio changed from 75% to 25. To the best of authors knowledge, the effect of baffle cut ratio configuration on acoustic response and back pressure has not been previously reported or investigated.

A study into the kinematic response for unbelted human occupants during emergency braking

ABSTRACT Since January 2014 more vehicles are being fitted with new active safety systems facilitating vehicle collision avoidance or mitigation by reducing the kinetic energy prior to impact, the most common being autonomous emergency braking systems. Although beneficial in reducing crash energy these safety features may influence the occupants posture within the cabin, and require special attention for the design and development of restraints system should the occupants be out of position or unbelted. This paper reviews the current reference volunteers’ physical test, proposed by Ejima, used to validate the unbelted kinematics of active human computer model and proposes a new set of generic biomechanical kinematic responses based on OM4IS sled test data, which are judged more representative to an unbelted occupants reaction. New kinematics corridors for head and torso angular change in a typical 1 ‘g’ frontal scenario are provided.

Optimization for Refinement of Vehicle Safety Structures

This purpose of this chapter is to demonstrate how vehicle safety structures can be optimized with an emphasis on occupant and pedestrian safety. This chapter focuses on size and variable optimization as opposed to topology optimization which has been the emphasis in the preceding chapters. The chapter will investigate means of optimizing a restraint system in the context of a frontal crash scenario by considering restraint system parameters. In the pedestrian scenario, the chapter will focus on the emerging technology of deployable bonnets and will investigate methods of optimizing the associated pyrotechnic lifting system.

Complications of Nonlinear Structural Optimization

This chapter focuses on some of the main issues relating to nonlinear optimization with an emphasis on topology optimization. This is specifically done by comparing and reviewing the equivalent static load method (ESLM) which is based on the VDM-SIMP approach presented in Chapter 4; ESLM was, however, explicitly developed for nonlinear topology optimization. ESLM has been successfully used for many topology optimization applications; the case studies of this chapter are, however, intended to expose the shortcomings of this approach, thereby also exposing many of the central issues relating to any finite element-based nonlinear topology optimization algorithm. These include, but are not limited to, parameter sensitivity, boundary condition modeling, scalability, as well as robustness and sensitivity studies in general. This chapter concludes with a direct comparison of linear static VDM-SIMP to ESLM, including further review of the case studies presented in Chapter 5 (Applications of Linear Optimization to Concept Vehicle Safety Structures).