Vehicle Design Highlights

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Title: Influence of a shock absorber model on vehicle dynamic simulation

Author(s): J A Calvo, B López-Boada, J L San Román, A Gauchía

Source: Proceedings of the I MECH E Part D Journal of Automobile Engineering

Volume: 223 Page: 189-203. February 2009

DOI: 10.1243/09544070JAUTO990

Publisher: Professional Engineering Publishing

Abstract: The dynamic simulation of mechanical systems is an essential tool in vehicle design. This work analyses the influence of a shock absorber model on a vehicle's dynamic behaviour by means of a simulation-based model. The real behaviour of a European medium-range car shock absorber has been obtained by means of a test rig. From the damper's real behaviour, three mathematical models were generated, increasing the complexity. An existing full vehicle simulation application (CarSim™) was used for this particular study. The vehicle's behaviour was analysed for typical driving manoeuvres taking into account lateral, vertical, and longitudinal forces and was compared with the results obtained with the different shock absorber models developed. As a result of this paper, it was demonstrated that, in order to obtain results with an acceptable level of accuracy, it is not necessary to rely on extremely complex shock absorber models.

Title: Detecting subtle cosmetic defects in automotive skin panels

Author(s): S Hazra, D Williams, R Roy, R Aylmore

Source: Proceedings of the I Mech E Part C Journal of Mechanical Engineering Science

Volume: 222 part 11, pages 2203-2207, November 2008

DOI:10.1243/09544062JMES910

Publisher: Professional Engineering Publishing

Abstract:
Cosmetic defects, such as ‘hollows’, are deviations in topology of automotive skin panels that form as a result of springback at the end of the forming process. These deviations are usually too small and local to be detected by discrete measurements of the panel but become visually apparent after the application of paint. As a result, the perceived quality of a panel may become unacceptable and considerable time may be dedicated to minimizing their occurrence through tool modifications. This paper proposes that there are three aspects to the problem. The first is the springback of the panel, the second is the optics of the painted panel, and the third is the ability of human sight to perceive a defect. In particular, it is argued that hollows cause optical distortions that inform the human eye of the presence of a defect. The paper then suggests that signal processing techniques, in particular the wavelet transform, provide a way to relate the geometry of a hollow to the resulting optical distortion. The transform was applied to two physical parts and the paper will discuss the effectiveness of the transform in locating and quantifying the relative severities of the defects that were present.

Title: Optimum design of an automotive inner door panel with a tailor-welded blank structure

Author(s): P Zhu, Y-L Shi, K-Z Zhang, Z-Q Lin

Source: Proceedings of the I Mech E Part D Journal of Automobile Engineering

Volume: 222 part 8, pages 1337-1348, August 2008

DOI: 10.1243/09544070JAUTO763

Publisher: Professional Engineering Publishing

Abstract:
This paper defines an integrated approach using finite element analysis, an artificial neural network (ANN), and a genetic algorithm (GA) for the optimization design of an inner door panel with a tailor-welded blank (TWB) structure, aiming at reducing the weight and enhancing the crashworthiness performances in side-impact collisions. In addition, strength and deformation resistance of the inner door panel are taken into account in the form of constraints in the optimization. First the governing equation of the central processing unit calculation time and the meshing method using the transition region is presented prior to the optimization process. Thus the dimension of the crash model can be controlled efficiently to prepare a fast-speed finite element model required for the later optimization. Then, in the initial design stage, a rough profile of the TWB structure is determined according to the distributions of the removed reinforcements around the inner door panel. Finally, the detailed design combines the ANN and the GA properly to provide an optimal combination of variables selected in the complicated multi-disciplinary problem. The optimal results indicate that the design framework presented here is outstanding with respect to the weight reduction and crashworthiness improvement.

Title: Modelling and ride dynamics of a flexible multi-body model of an urban bus

Author(s): G Georgiou, A Badarlis, S Natsiavas

Source: Proceedings of the I Mech E Part K Journal of Multi-body Dynamics

Volume: 222 part 2, pages 143-154, April 2008

DOI: 10.1243/14644193JMBD130

Publisher: Professional Engineering Publishing

Abstract:
Dynamic response of a large order mechanical model of an urban bus is investigated in this paper. The emphasis is first put on developing a quite complete model, which can be utilized in order to extract sufficiently reliable and accurate information related to its dynamics in a fast way. Since some of the components of the bus undergo large rigid body rotation, in addition to motion resulting from their deformability, a multi-body dynamics framework is adopted. This implies that the resulting equations of motion appear in the form of a strongly non-linear set of differential-algebraic equations, which are difficult to handle even numerically. In fact, the modelling becomes more involved because all the significant non-linearities appearing in the interconnections of the structural components and especially in the front and rear suspension subsystems of the bus are taken into account. In order to alleviate some of these complexities, the number of degrees of freedom of each component, associated with its deformability, is reduced drastically by applying an appropriate coordinate condensation methodology. Finally, this model is employed and numerical results are obtained for motions resulting from typical road excitation. In particular, selected response quantities related to ride comfort are examined for characteristic combinations of the bus suspension stiffness and damping parameters.

Title: Analytical prediction of springback based on residual differential strain during sheet metal bending

Author(s): H K Yi, D W Kim, C J Van Tyne, Y H Moon

Source: Proceedings of the I Mech E Part C Journal of Mechanical Engineering Science

Volume: 222 part 2, pages 117-129, Feb 2008

DOI: 10.1243/09544062JMES682

Publisher: Professional Engineering Publishing

Abstract: As the springback of sheet metal during unloading may cause deviation from a desired shape, accurately predicting springback is essential for the design of sheet stamping operations. Finite-element models have not been successful in predicting springback; hence there is a need for analytical models to make such predictions. In this study, a model based on differential strains after relief from the maximum bending stress is derived for six different deformation patterns in order to predict springback analytically. The springback for each deformation pattern is estimated by the residual differential strains between outer and inner surfaces after elastic recovery. Each of the six deformation patterns has a valid region of applicability, based on elastic modulus, yield strength, applied tension, and bending geometry. Analytical equations for the springback of the sheet deformed under these six deformation patterns are derived. Traditional analytical models for springback prediction have been based on elastic unloading from a bending moment. Traditional models also require the knowledge of the stress distribution through the thickness of the sheet, whereas the residual differential strain model only requires the stress state on the outer and inner surfaces of the sheet. In order to compare the residual differential strain model with the traditional bending moment model, a bending moment model is derived for the same exact deformation patterns. Results from the two models are compared for various materials.

Title: A study of the simulation of a front-crash-induced rollover crash

Author(s): C. Jiang, C.E. Neal-Sturgess

Source: Proceedings of the I Mech E Part D Journal of Automobile Engineering

Volume: 221 part 12, pages 1487-1497, Dec 2007

DOI: 10.1243/09544070JAUTO628

Publisher: Professional Engineering Publishing

Abstract: Computer-based simulation of rollover using MADYMO can assist in understanding the occupant and vehicle kinematics of these complex long-duration events, and the resulting occupant injuries. This study focused on the simulation of a front-crash-induced rollover event. A hybrid finite element (FE)-rigid body model of the vehicle was created to simulate the deformation during the impact and its influence on the following rollover event. This was used, together with a multi-body MADYMO model of a Hybrid III dummy, to evaluate the probability of head injury in the crash. Special attention was paid to the modelling of the suspension and tyres. Simulation results from both the FE model and the rigid body model were validated and evaluated. The results indicate that rollover simulations using MADYMO proved to be an efficient computer aided engineering (CAE) methodology. It is necessary to have a deformable FE front end for the vehicle to simulate this type of event accurately. The injury parameters from the simulation correlate well with the injury results from the crash report.

Title: Simulation of distortion induced in assemblies by spot welding

Author(s): X Fan, I Masters, R Roy, D Williams

Source: Proceedings of the I MECH E Part B Journal of Engineering Manufacture

Volume: 221 Page: 1317-1326. August 2007

DOI: 10.1243/09544054JEM782

Publisher: Professional Engineering Publishing

Abstract: Maintaining dimensional tolerances during the manufacture of vehicle bodies is important to the automotive sector. With the industry's drive towards continuous improvement there is increasing focus on the effect of the joining process on the final assembly. A simulation tool that can predict the distortion resulting from assembly offers potential time- and cost-savings throughout design and manufacture. Although individual spot welds have been studied in detail, to-date methods to predict the distortion of a final assembly have concentrated on the variation of the constituent components. In the current paper simulation is used to predict the distortion of an assembly owing to spot welding using a local/global approach where the local distortion occurring around a single spot weld is projected onto a global assembly at each of the weld locations. The comparisons of the simulations of the assemblies with coordinate measuring machine (CMM) data under different clamping conditions suggest sufficient agreement with experimental data to be of value to engineers. A number of possible enhancements are suggested to improve the accuracy of final shape prediction.

Title: A hybrid method for feature recognition in computer-aided design models

Author(s): S S Dimov, E B Brousseau, R Setchi

Source: Proceedings of the I MECH E Part B Journal of Engineering Manufacture

Volume: 221 No 1 Page: 79-96. Jan 2007

DOI: 10.1243/09544054JEM437

Publisher: Professional Engineering Publishing

Abstract: Automatic feature recognition (AFR) techniques applied to three-dimensional (3D) solid models are an important tool for achieving a true integration of computer-aided design (CAD) and computer-aided manufacturing (CAM) processes. In particular, AFR systems allow the identification in CAD models of high-level geometrical entities: features that are semantically significant for manufacturing operations. However, the recognition performances of most of the existing AFR systems are limited to the requirements of specific manufacturing applications. This paper presents a new hybrid method that facilitates the deployment of AFR systems in different application domains. In particular, the method includes two main processing stages: learning and feature recognition. During the learning stage, knowledge acquisition techniques are applied for generating feature-recognition rules and feature hints automatically from training data. Then, these hints and rule bases are utilized in the feature-recognition stage to analyse boundary representation (B-Rep) part models and identify their feature-based internal structure. The proposed AFR method is implemented within a prototype feature-recognition system and its capabilities are verified on two benchmarking parts.

Title: Development of CAD models from sketches: a case study for automotive applications

Author(s): R Vignesh, R Suganthan, K Prakasan

Source: Proceedings of the I MECH E Part D Journal of Automobile Engineering

Volume: 221 No 1 Page: 41-47. Jan 2007

DOI: 10.1243/09544070JAUTO331

Publisher: Professional Engineering Publishing

Abstract: Today products are designed not only for their functional requirements but also for aesthetics. In the automotive industries, styling has become a major part of the design process with class-A surfaces. Class-A surfaces are freeform surfaces with a continuous curvature. The process of engineering any component or system begins by generating a concept that actually describes the product in terms of its form, function, and fit. Concept sketches help the designers to arrive quickly and easily at a stage where a satisfactory design can be specified for detailed design. These concept sketches can be used for development of the digital concept design and analysis of the curves and surfaces. Software such as Alias exists and thus can be used with suitable hardware for sketching the concept of the car body on a computer screen. In this paper a systematic procedure is discussed for generating class-A surfaces from the images of concept sketches which are manually prepared on paper. These images are imported into the sketch tracer module of CATIA V5. A designer can use the image as the reference and produce a digital sketch by tracing the image using CATIA V5 software without adding any special hardware. Later, interrogation of these surfaces for improved aesthetics can be attempted. This method will be useful for the users of CATIA V5 to improve their design practices and skills.

Title: Robust Design of an Automobile Front Bumper Using Design of Experiments

Author(s): Kwon-Hee Lee, Il-Kwon Bang

Source: Proceedings of the I MECH E Part D Journal of Automobile Engineering

Volume: 220 Page: 1199-1207. Sept 2006

DOI: 10.1243/09544070JAUTO311

Publisher: Professional Engineering Publishing

Abstract: Bumpers are structural components installed to reduce physical damage to the front and rear ends of a passenger motor vehicle from low-speed collisions. Damage and protection assessments are the commonly used design criteria in bumper design. For damage assessment, the relative displacements representing stiffness performance are defined and examined. At the protodesign stage for a new car, finite element (FE) analysis is often utilized to predict the stiffness of a bumper. However, conventional bumper analysis through FEM outputs a constant stiffness even though the stiffness has some distribution due to uncertainties. In this research, the uncertainties are assumed to be the tolerances of thicknesses. Under this uncertain condition, the displacements representing stiffness are calculated by approximate statistics and by worst-case analysis. Then, a robust design is determined by design of experiments (DOE) using the orthogonal array strategy to find the design having a minimum weight of bumper within the stiffness constraints. In this research, the thicknesses of the inner beam, outer beam, and stay are treated as design variables. The robust design procedure for a bumper, considering the uncertain thicknesses, is presented.

Title: Aerodynamics of a wing in ground effect in generic racing car wake flows

Author(s): M D Soso, P A Wilson

Source: Proceedings of the I MECH E Part D Journal of Automobile Engineering

Volume: 220 Page: 1-13. Jan 2006

DOI: 10.1243/095440705X69632

Publisher: Professional Engineering Publishing

Abstract: In an effort to provide more detailed insight into the aerodynamic factors that may influence the creation of overtaking opportunities in modern open-wheeled racing series, a set of wind tunnel experiments was initiated in the moving ground facilities at the University of Southampton. To generate data typical of one car following another, a single-element wing in ground effect was tested downstream of a bluff body that incorporated a diffuser and rear wing. The tests included variations in the height and angle of attack of the wing, while data collection was achieved via force and pressure measurements, flow visualization and flowfield surveys. The results were then compared with baseline data that were obtained without the presence of the bluff body. It was found that, while behind the upstream body, the wing experienced a decrease in its downforce values, with the amount of downforce lost depending on its height above the ground. It was also shown that more downforce was lost from sections closer to the mid-span of the wing than was the case from sections closer to the tips of the wing.

Title: Effect of moving surface on the aerodynamic drag of road vehicles

Author(s): S N Singh; L Rai; P Puri; A Bhatnagar

Source: Proceedings of the I MECH E Part D Journal of Automobile Engineering

Volume: 219 Page: 127 - 134. Feb 2005

DOI: 10.1243/095440705X5886

Publisher: Professional Engineering Publishing

Abstract: The effect on aerodynamic drag using a model of a truck has been investigated by controlling the boundary layer separation by the momentum injection method using a rotating cylinder. It involves the use of experiments coupled with computational fluid dynamics (CFD) analysis to validate the theory of momentum injection. Modelling of the truck has been done on the software GAMBIT© . The best suitable turbulence model was selected by comparing the results with the experimental results. The rotational speed and radius of the cylinder are varied to establish the effect of momentum injection on aerodynamic drag. The coefficient of drag reduces by approximately 35 per cent from an initial value of 0.5-0.32 for a cylinder of radius 1 cm with rotational speed of 4000 r/min.