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The in-wheel motor (IWM) is a promising advancement in electric vehicle propulsion since it offers greater packaging efficiency and torque vectoring capabilities than a chassis-mounted motor. However, the increased unsprung mass degrades the vehicle dynamics by increasing body vertical acceleration (BVA) and tyre dynamic load (TDL), worsening ride comfort and road-holding respectively. Another important consideration is magnetic gap deformation (MGD), which results from the deflection between the motor stator and rotor. Reducing MGD improves the motor reliability and longevity. This paper addresses these issues by incorporating inerters into an existing IWM model. They are incorporated into the strut and bushes to control BVA, TDL and MGD. The system optimised for MGD resulted in a deflection reduction of over 98% without compromising performance of the other indices. Optimising the strut and bushes for BVA and TDL reduced them by 20% and 9% respectively without degrading MGD. A sensitivity analysis of the results is presented. Here the damping and inertance values are varied by 20% from the optimum, and the resulting performance still improves upon the default. It is concluded that there are significant potential improvements where inerters are included in an in-wheel motor system. [ABSTRACT FROM AUTHOR]

Shimmy is one of the important factors affecting the ride comfort and lateral stability of straddle-type monorail vehicles with single-axle bogies (SMVS). To obtain the main parameters affecting SMVS shimmy, a global sensitivity analysis strategy for SMVS shimmy is proposed. The shimmy response surface model is constructed, and the sensitivity analysis of the shimmy response surface model is carried out by the Sobol method. Based on this, the shimmy factor model of SMVS is established by factor analysis method. A novel SMVS shimmy analysis method based on factor model is proposed. The shimmy factor model is verified by the dynamic model of SMVS. The results show that 11 main factors affecting the shimmy are obtained by sensitivity analysis. Through the dimension reduction technology of factor analysis, four main factors affecting SMVS shimmy are extracted. The complex coupling relationship between the shimmy factors of SMVS is revealed. The established shimmy factor model can effectively analyse the shimmy state of SMVS, and the dynamic simulation results also show consistency. This study not only proposes a new perspective to understand the SMVS shimmy mechanism, but also provides the foundation for further optimal design of monorail vehicle stability. [ABSTRACT FROM AUTHOR]

In the condition of actual obstacle avoidance, where longitudinal deceleration is large and variable, it is difficult for the autonomous vehicle to simultaneously track longitudinal velocity and lateral motion. In addition, when the planned trajectory exceeds the adhesion of the road, the vehicle is also prone to losing stability. Most studies of the obstacle avoidance process only consider constant velocity. This paper presents a novel control architecture for four-wheel driving (4WD) and four-wheel steering (4WS) autonomous vehicles to track predefined trajectory and velocity. It is proposed to use preview technology to obtain the desired state of the vehicle and a controller based on multi-input multi-output nonlinear model predictive control (MIMO-NMPC) that considers the deceleration-steering combination condition. According to the sensitivity analysis of the influence of tyre slip rate on tyre lateral force, the optimal working boundary of the tyre is determined. The output of the controller is constrained by estimating tyre force to prevent tyre force saturation and maximise tyre adhesion limit utilisation. The simulation results demonstrate that the proposed controller can better track the trajectory and longitudinal velocity with a faster response on the high-adhesion road. The overshoot of lateral displacement and the maximum error of longitudinal velocity are less than 0.03m and 0.2m/s, respectively. In addition, when the planned trajectory exceeds the adhesion limit of the road, it can still follow the desired trajectory as closely as possible while maintaining stability on low-adhesion roads. [ABSTRACT FROM AUTHOR]

This paper presents a non-linear integrated control strategy that primarily focuses maintaining vehicle lateral stability using active front steering and differential braking. The proposed control strategy utilises a non-linear model predictive controller to improve lateral stability. A stable linear reference model is used for reference generation. By including the understeer gradient in the reference model, different kinematic responses are obtained from the controlled vehicle. The prediction model utilises the road friction estimate to create dynamic stability constraints that include rollover and sliding of the vehicle. The design of the model predictive controller allows easy activation of different control actuators and dynamic modification to the control behaviour. The control methodology is validated using MATLAB/Simulink and a validated MSC ADAMS model. A sensitivity analysis is conducted to identify the susceptibility of the control strategy to various parameters and states. [ABSTRACT FROM AUTHOR]

In this study, dynamic models of three bogies— traditional bogie (TB), active steering bogie (ASB), and forced steering bogie (FSB) —were established to clarify the similarities and differences between them in the parameter optimization design of dynamic performance. The first- and second-order sensitivities of the effects of the vehicle dynamic parameters on the wear, running stability, and riding comfort were obtained based on the global sensitivity method. According to the results of sensitivity analysis, the ASB and FSB primarily focus on changing the steering mechanism of the TB in the curved track and have insignificant effect on the running stability and riding comfort. Next, the dynamic performances of the three vehicles were evaluated using the control variable method. The results indicate that the ASB and FSB could change the parameter optimization method of TB, mainly because the contradiction between wear and running stability need not be considered when key parameters are in the feasible region, and the optional range of parameters is further widened. Finally, parameter optimization methods for different vehicles were formulated based on a comprehensive dynamic performance function. [ABSTRACT FROM AUTHOR]

Railway vehicle dynamics is strongly affected by track irregularities, which can influence the safety and the running behaviour of the vehicle. The EN 13848-5:2017 standard provides the limits of track irregularities for standard track but does not states specific restrictions for switches and crossings. Furthermore, since turnouts have a limited length, their track geometric irregularities cannot be accurately described by stochastic functions usually adopted for railway vehicle dynamics simulations. Nevertheless, irregularities in railway turnouts, related to the non-uniform stiffness of the track support and to the variation of the rail profiles along the longitudinal direction should be considered in dynamic simulations, as they can generate large dynamic loads, strongly affecting the vehicle dynamics and running stability. The aim of the paper is to expand the Switches and Crossing benchmark exercise analysing the effect of several kinds of irregularity with different wavelengths and amplitudes on a complete turnout on the main quantities related to the vehicle dynamics. The influence of each defect on each quantity is estimated through a post-processing sensitivity analysis based on power spectral density calculation. This sensitivity analysis is hence used to combine different types of defects in order to detect irregularity combinations that could compromise running safety. [ABSTRACT FROM AUTHOR]

Suspension parameters optimisation and matching is a very important topic in the design of railway vehicles, and a reasonable combination of suspension parameters is the most powerful guarantee for safe and stable operation. However, most of the existing research about that still belongs to single-objective optimisation and pays little attention to the matching relationship between different suspension parameters, which has plenty of limitations. Therefore, the lateral stability and ride comfort of a certain type of domestic high-speed locomotive are studied and optimised through the genetic algorithm NSGA-II, to find the optimal lateral dynamic performance. It can be found that there is an obvious contradiction between linear stabilities under low-conicity and high-conicity conditions, but a strong positive correlation between low-conicity stability and lateral ride comfort in a low-conicity condition. Besides, the matching relation of the six key suspension parameters is explored employing data analysis methods, such as global sensitivity and clustering analysis, and three types of parameter combinations are proposed. In addition, the speed robustness and rail cant robustness regarding the three types of parameter combinations are analyzed, and the lateral dynamic performance characteristics of each parameter combination type are summarised. [ABSTRACT FROM AUTHOR]

Crosswinds affect vehicle driving stability and their influence increase with driving speed. To improve high speed driving stability, interdisciplinary research using unsteady aerodynamics and vehicle dynamics is necessary. The current demands of faster development times require robust virtual methods for assessing stability performance in early design phases. This paper employs a numerical one-way coupling between the two disciplines and uses a variety of realistic crosswind gust profiles for the aerodynamic simulations to output representative forces and moments on three vehicle dynamic models of different fidelity levels, ranging from a one-track model to a full multi-body dynamic model of a sports utility vehicle. An investigation on required model fidelity was conducted along with a sensitivity study to find key aerodynamic and vehicle dynamic characteristics to minimise the yaw velocity and lateral acceleration response during crosswinds. Transient aerodynamic simulations were used to model crosswind gusts at high speeds. Analysis of the forces and moments showed that rapid changing gusts generate overshoots in the yaw moment, due to the phase delay of the flow between the front and rear of the vehicle. A methodology for modelling this phase delay is proposed. The response of the vehicle was captured equally well by the enhanced model (mid-level fidelity) and the full multi-body dynamic model, while the simplest one-track model failed to emulate the correct vehicle response. The sensitivity study showed the importance of the positioning of the centre of gravity, the aerodynamic coefficient of yaw moment, wheel base, vehicle mass and yaw inertia. In addition, the axles' side force steer gradients and other suspension parameters revealed potential in improving crosswind stability. [ABSTRACT FROM AUTHOR]

In this paper, a hierarchical optimization strategy for an ambulance with a supine human body model is proposed to improve suspension performance, where the ride comfort of both patients and paramedics and the road holding of the ambulance vehicle are particularly focused. An ambulance model integrating a hydraulically interconnected suspension system and a stretcher-human body model is developed first. This integrated model considers the interaction between stretcher and human body and provides a platform to directly evaluate ride comfort of patients. The sensitivity stratification concept is defined and the sensitivity levels of each design variable are determined according to sensitivity ratios. Then, design variables and optimization objectives are divided into two pairs and optimized in sequence, which not only comprehensively considers the overall performance of patients and paramedics, but also reduces the number of objectives in each optimization process. At last, the optimum solution of proposed hierarchical strategy is obtained and compared with general monolayer optimization strategy. The simulation results show that the hierarchical strategy is highly competitive and outperforms the monolayer optimization strategy, being able to provide not only a better solution and convergence but also has good computational efficiency. [ABSTRACT FROM AUTHOR]

This study aims to provide quantitative insight into the sensitivity of tyre parameters on the performance of the anti-lock braking system (ABS) control algorithms. Unlike conventional sensitivity analysis methods, which depend on a few test cases, in this study, Magic Formula (MF) 6.1 tyre model is used to generate a comprehensive set of thousands of virtual tyres that encompasses all possible combinations of the four main longitudinal parameters. To broaden the scope of impact of this study, two ABS controllers – one based on wheel spin acceleration (literature version of Bosch ABS) and the other based on sliding mode control (SMC) are designed in MATALB-Simulink ® and integrated with IPG Carmaker ® to perform complete vehicle dynamics simulations. Straight-line ABS simulations are performed on dry asphalt road using both the controllers and each test-run is performed for five different set-point longitudinal slip ratios ( λ r e f ). The results of the conditional variance-based sensitivity analysis consisting of 211,250 simulation tests indicate that the tyre peak friction coefficient and shape factor have significant contributions to ABS stopping distance. The sensitivity for stopping distance to tyre parameters varies amongst the controllers. While with Bosch algorithm parameter D almost completely controls the stopping distance, the sliding mode ABS is sensitive to parameters λ r e f , C and D. Tyre parameter interactions indicated by the factor K = B ∗ C ∗ D , though hard to visually interpret, is expounded using global sensitivity analysis metrics. [ABSTRACT FROM AUTHOR]

An extended Dichotomy method is proposed for an accurate determination of the critical speed of railway vehicles. The high-dimensional Hermite orthogonal polynomial (HOP) based on the independent and normal distribution parameters is derived. Both the Monte Carlo (MC) method based on a Latin hypercube sampling (LHS) and the HOP expansion method using different collocation methods are compared to investigate the statistical characteristics of the critical speed of a Chinese railway bogie. After that, the relation between the critical speed and the random input parameters is approximately constructed. The relation is then used to conduct a relative local sensitivity analysis (LSA), a global sensitivity analysis (GSA) and a regional sensitivity analysis (RSA) of the bogie. It is indicated that RSA is a good method for sensitivity analysis of the critical speed due to its good efficiency and trusty precision. The results also show that the secondary lateral damper is the most important parameter to the critical speed for this bogie. By increasing its values and reducing its variation range, the critical speed can be increased and the variation is decreased. It may offer some instructions and practical values for vehicle design, operation, and comprehensive evaluation of the stability of railway vehicles. [ABSTRACT FROM AUTHOR]

This paper is devoted to present an integrated uncertainty and sensitivity procedure for use in performance assessments for train–bridge interactions. Firstly, a train-ballasted track–bridge dynamic model with proper consideration of the nonlinear wheel–rail contact geometries is constructed in three-dimensional space; and then the uncertainties related to this system are illustrated, in which the material, geometry, structural damping of bridge superstructure and the temporal–spatial ergodic properties of track irregularities are highlighted; and furthermore, the probability density evolution method accompanied with an advanced number theoretical method is introduced to describe the transmission of probability from excitation input to response output for the uncertainty analysis; finally, the key factors affecting the dynamic behaviours of system components are clarified by the variance-based global sensitivity analysis which has taken the interactions between factors into account. Numerical examples show that the uncertainty analysis algorithm is of high efficiency and accuracy by comparing with the robust Monte-Carlo simulation method; the variability of bridge parameters and track irregularities show remarkable effects on the dynamic indices; and the most sensitive factors are rather different with regard to varied dynamic indices. [ABSTRACT FROM AUTHOR]

The dynamic parameters of Straddle-type monorail vehicles with single-axle bogies are optimised by utilising the multi-body dynamic method. The dynamic parameter optimisation is conducted aiming at the curve negotiation properties, comfort and tire eccentric wear of monorail vehicles. The optimisation model is established with software ADAMS and modeFRONTIER and the Sobol is adopted for sensitivity analysis to acquire the optimised parameters. Finally, the multiobjective collaborative optimisation algorithm is utilised for optimised analysis. According to the results, the proposed method can conduct multi-objective optimisation to the monorail vehicles in a successful way. The curve negotiation properties and comfort are improved, and the tire wear is reduced with dynamic parameters after optimisation. Especially, a conversion strategy of the consistent objective function is proposed aiming at multiobjective nonlinear convergence. [ABSTRACT FROM AUTHOR]

This paper proposes a novel 2-step global sensitivity analysis algorithm to provide an in-depth sensitivity analysis of the vehicle parameters on the system responses. A 9 degree-of-freedom nonlinear vertical–lateral coupled vehicle model is developed, and 12 parameters along with 7 system responses are selected for the sensitivity analysis. In order to reduce the computational effort, the proposed 2-step algorithm calculates the elementary effects and selects 7 influential parameters from these 12, and then uses the Sobol' method to obtain the global sensitivity indexes of these influential parameters. An unscented Kalman filter is finally designed to show the effect and importance of the selected sensitive parameters on the observation accuracy. Simulations with different vehicle types, velocities and tyre models have verified that the proposed algorithm can accurately describe the relationship between the vehicle parameters and system responses, which is of directive significance to improve vehicle controller and observer performances. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is presented for investigating suspension bushing based on mechanical properties of the bushing, their effective directions, spring stiffness and damping coefficient of bushing. The vehicle vibration model and suspension geometry parameters are used to optimise the vehicle suspension based on multi-body dynamics simulation (ADAMS/CAR) initially. Several experiment tests based on ISO 4128 and ISO 7401 have been performed in one of main Iranian automaker (SAIPA) in order to verify the ADAMS/CAR model. The grey relational analysis based on using Taguchi L27 orthogonal array is used to obtain the optimum suspension. Then the bushing characteristics are optimised considering the indicated method. This method considers a combination of ride comfort and handling qualities of vehicle as objective functions simultaneously. The results of optimum suspension are compared with typical Renault Logan which declares the accuracy and efficiency of this method in optimising suspension bushing. [ABSTRACT FROM AUTHOR]

This study investigates the coupled ride and directional performance characteristics of an articulated frame-steered vehicle (AFSV). A three-dimensional multi-body dynamic model of the vehicle is formulated integrating the hydro-mechanical frame steering and hydro-pneumatic suspension (HPS) systems. The model parameters are obtained from field-measured data acquired for an unsuspended AFSV prototype and a validated scaled HPS model. The HPS is implemented only at the front axle, which supports the driver cabin. The main parameters of the HPS, including the piston area, and flow areas of bleed orifices and check valves, are selected through design sensitivity analyses and optimisation, considering ride vibration, and roll- and yaw-plane stability performance measures. These include the frequency-weighted vertical vibration of the front unit, root-mean-square lateral acceleration during the sustained lateral load transfer ratio period prior to absolute rollover of the rear unit, and yaw-mode oscillation frequency following a lateral perturbation of the vehicle. The results suggested that the implementation of the HPS to the front unit alone could help preserve the directional stability limits compared to the unsuspended prototype vehicle and reduce the ride vibration exposure by nearly 30%. The results of sensitivity analyses revealed that the directional stability performance limits are only slightly affected by the HPS parameters. Further reduction in the ride vibration exposure was attained with the optimal design, irrespective of the payload variations. The vehicle operation at relatively higher speeds, however, would yield greater vibration exposure. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of the track geometry irregularities on the wheel-rail dynamic interactions and the rail fatigue initiation through the application of the Dang Van criterion, that supposes an elastic shakedown of the structure. The irregularities are modelled, using experimental data, as a stochastic field which is representative of the considered railway network. The tracks thus generated are introduced as the input of a railway dynamics software to characterise the stochastic contact patch and the parameters on which it depends: contact forces and wheelset-rail relative position. A variance-based global sensitivity analysis is performed on quantities of interest representative of the dynamic behaviour of the system, with respect to the stochastic geometry irregularities and for different curve radius classes and operating conditions. The estimation of the internal stresses and the fatigue index being more time-consuming than the dynamical simulations, the sensitivity analysis is performed through a metamodel, whose input parameters are the wheel-rail relative position and velocity. The coefficient of variation of the number of fatigue cycles, when the simulations are performed with random geometry irregularities, varies between 0.13 and 0.28. In a large radius curve, the most influent irregularity is the horizontal curvature, while, in a tight curve, the gauge becomes more important. [ABSTRACT FROM AUTHOR]

Objective measurements and computer-aided engineering simulations cannot be exploited to their full potential because of the high importance of driver feel in vehicle development. Furthermore, despite many studies, it is not easy to identify the relationship between objective metrics (OM) and subjective assessments (SA), a task further complicated by the fact that SA change between drivers and geographical locations or with time. This paper presents a method which uses two artificial neural networks built on top of each other that helps to close this gap. The first network, based solely on OM, generates a map that groups together similar vehicles, thus allowing a classification of measured vehicles to be visualised. This map objectively demonstrates that there exist brand and vehicle class identities. It also foresees the subjective characteristics of a new vehicle, based on its requirements, simulations and measurements. These characteristics are described by the neighbourhood of the new vehicle in the map, which is made up of known vehicles that are accompanied by word-clouds that enhance this description. This forecast is also extended to perform a sensitivity analysis of the tolerances in the requirements, as well as to validate previously published preferred range of steering feel metrics. The results suggest a few new modifications. Finally, the qualitative information given by this measurement-based classification is complemented with a second superimposed network. This network describes a regression surface that enables quantitative predictions, for example the SA of the steering feel of a new vehicle from its OM. [ABSTRACT FROM PUBLISHER]

Vehicle driveability describes the complex interactions between the driver and the vehicle, mainly related to longitudinal vibrations. Today, a relevant part of the driveability process optimisation is realised by means of track tests, which require a considerable effort due to the number of parameters (such as stiffness and damping components) affecting this behaviour. The drawback of this approach is that it is carried on at a stage when a design iteration becomes very expensive in terms of time and cost. The objective of this work is to propose a light and accurate tool to represent the relevant quantities involved in the driveability analysis, and to understand which are the main vehicle parameters that influence the torsional vibrations transmitted to the driver. Particular attention is devoted to the role of the tyre, the engine mount, the dual mass flywheel and their possible interactions. The presented nonlinear dynamic model has been validated in time and frequency domain and, through linearisation of its nonlinear components, allows to exploit modal and energy analysis. Objective indexes regarding the driving comfort are additionally considered in order to evaluate possible driveability improvements related to the sensitivity of powertrain parameters. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to propose a new method for designing Macpherson suspension, based on the Sobol indices in terms of Pearson correlation which determines the importance of each member on the behaviour of vehicle suspension. The formulation of dynamic analysis of Macpherson suspension system is developed using the suspension members as the modified links in order to achieve the desired kinematic behaviour. The mechanical system is replaced with an equivalent constrained links and then kinematic laws are utilised to obtain a new modified geometry of Macpherson suspension. The equivalent mechanism of Macpherson suspension increased the speed of analysis and reduced its complexity. The ADAMS/CAR software is utilised to simulate a full vehicle, Renault Logan car, in order to analyse the accuracy of modified geometry model. An experimental 4-poster test rig is considered for validating both ADAMS/CAR simulation and analytical geometry model. Pearson correlation coefficient is applied to analyse the sensitivity of each suspension member according to vehicle objective functions such as sprung mass acceleration, etc. Besides this matter, the estimation of Pearson correlation coefficient between variables is analysed in this method. It is understood that the Pearson correlation coefficient is an efficient method for analysing the vehicle suspension which leads to a better design of Macpherson suspension system. [ABSTRACT FROM PUBLISHER]

A nonlinearity-induced time-varying harmonic dynamic axle load is found in the road test of a car–trailer combination. To understand its influence on system dynamic stability, a corresponding linear single-track model (STM) is proposed. System dynamic stability is described and sensitivity analysis for the system parameters is achieved. The contribution of the harmonic force is quantified by a derived effective axle load. Because the harmonic effect might be time varying in practice, a time–frequency analysis-based parameter identification method is introduced. Experimental study shows that a time-varying harmonic effect really exists. A yaw-rate-based simulation method is designed to simulate this behaviour. The sensitivity analysis of the influence of the harmonic amplitude or phase on dynamic stability is performed with a simulation study. With appropriate modification of the harmonic amplitude and phase shift applied in selected time windows, the time-varying system characteristics in the road test can be simulated very well. [ABSTRACT FROM AUTHOR]

To improve safety and maximum admissible speed on different operational scenarios, multiobjective optimisation of bogie suspension components of a one-car railway vehicle model is considered. The vehicle model has 50 degrees of freedom and is developed in multibody dynamics software SIMPACK. Track shift force, running stability, and risk of derailment are selected as safety objective functions. The improved maximum admissible speeds of the vehicle on curves are determined based on the track plane accelerations up to 1.5 m/s2. To attenuate the number of design parameters for optimisation and improve the computational efficiency, a global sensitivity analysis is accomplished using the multiplicative dimensional reduction method (M-DRM). A multistep optimisation routine based on genetic algorithm (GA) and MATLAB/SIMPACK co-simulation is executed at three levels. The bogie conventional secondary and primary suspension components are chosen as the design parameters in the first two steps, respectively. In the last step semi-active suspension is in focus. The input electrical current to magnetorheological yaw dampers is optimised to guarantee an appropriate safety level. Semi-active controllers are also applied and the respective effects on bogie dynamics are explored. The safety Pareto optimised results are compared with those associated with in-service values. The global sensitivity analysis and multistep approach significantly reduced the number of design parameters and improved the computational efficiency of the optimisation. Furthermore, using the optimised values of design parameters give the possibility to run the vehicle up to 13% faster on curves while a satisfactory safety level is guaranteed. The results obtained can be used in Pareto optimisation and active bogie suspension design problems. [ABSTRACT FROM PUBLISHER]

This article suggests a strategy to control semi-active suspensions of vehicles in a pro-active way to adapt to future road profiles. The control strategy aims to maximise comfort while maintaining good handling properties. It employs suitably defined optimal control problems in combination with a parametric sensitivity analysis. The optimal control techniques are used to optimise the time-dependent damper coefficients in an electro-rheological damper for given nominal road profiles. The parametric sensitivity analysis is used to adapt the computed nominal optimal controls to perturbed road profiles in real time. The method is particularly useful for events with a low excitation frequency such as ramps, bumps, or potholes. For high-frequency excitations standard controllers are preferable; so we propose a switched open–closed-loop controller design. Various examples demonstrate the performance of the approach. [ABSTRACT FROM AUTHOR]

This paper presents the objectification techniques for the assessment of steering feel including {on-centre} feel and steering response by measurement data. Here, new objective parameters are developed by considering not only the process by which the steering feel is evaluated subjectively but also by the ergonomic perceptive sensitivity of the driver. In order to validate such objective parameters, subjective tests are carried out by professional drivers. Objective measurements are also performed for several cars at a proving ground. The linear correlation coefficients between the subjective ratings and the objective parameters are calculated. As one of new objective parameters, steering wheel angle defined by ergonomic perception sensitivity shows high correlation with the subjective questionnaires of on-center responses. Newly defined steering torque curvature also shows high correlation with the subjective questionnaires of on-center effort. These correlation results conclude that the subjective assessment of steering feel can be successfully explained and objectified by means of the suggested objective parameters. [ABSTRACT FROM AUTHOR]

In certification of new rail vehicles with respect to running characteristics, a wide variety of operating conditions needs to be considered. However, in associated test runs the wheel–rail friction condition is difficult to handle because the friction coefficient needs to be fairly high and the friction is also generally hard to assess. This is an issue that has been studied in the European project DynoTRAIN and part of the results is presented in this paper. More specifically, an algorithm for estimating the wheel–rail friction coefficient at vehicle certification tests is proposed. Owing to lack of some measurement results, the algorithm here is evaluated in a simulation environment which is also an important step towards practical implementation. A quality measure of the friction estimate is suggested in terms of estimated wheel–rail spin and total creep. It is concluded that, tentatively, the total creep should exceed 0.006 and the spin should be less than 1.0 m−1for the algorithm to give a good friction estimate. Sensitivity analysis is carried out to imitate measurement errors, but should be expanded in further work. [ABSTRACT FROM AUTHOR]

We present an approach to global sensitivity analysis aiming at the reduction of its computational cost without compromising the results. The method is based on sampling methods, cubature rules, high-dimensional model representation and total sensitivity indices. It is applied to a half car with a two-axle Cooperrider bogie, in order to study the sensitivity of the critical speed with respect to the suspension parameters. The importance of a certain suspension component is expressed by the variance in critical speed that is ascribable to it. This proves to be useful in the identification of parameters for which the accuracy of their values is critically important. The approach has a general applicability in many engineering fields and does not require the knowledge of the particular solver of the dynamical system. This analysis can be used as part of the virtual homologation procedure and to help engineers during the design phase of complex systems. [ABSTRACT FROM AUTHOR]

A numerical model to predict train-induced vibrations is presented. The dynamic computation considers mutual interactions in vehicle/track coupled systems by means of a finite and discrete elements method. The rail defects and the case of out-of-round wheels are considered. The dynamic interaction between the wheel-sets and the rail is accomplished by using the non-linear Hertzian model with hysteresis damping. A sensitivity analysis is done to evaluate the variables affecting more the maintenance costs. The rail–sleeper contact is assumed extended to an area-defined contact zone, rather than a single-point assumption which fits better real case studies. Experimental validations show how prediction fits well experimental data. [ABSTRACT FROM PUBLISHER]

This work describes an analytical approach to determine what degree of accuracy is required in the definition of the rail vehicle models used for dynamic simulations. This way it would be possible to know in advance how the results of simulations may be altered due to the existence of errors in the creation of rolling stock models, whilst also identifying their critical parameters. This would make it possible to maximise the time available to enhance dynamic analysis and focus efforts on factors that are strictly necessary. In particular, the parameters related both to the track quality and to the rolling contact were considered in this study. With this aim, a sensitivity analysis was performed to assess their influence on the vehicle dynamic behaviour. To do this, 72 dynamic simulations were performed modifying, one at a time, the track quality, the wheel–rail friction coefficient and the equivalent conicity of both new and worn wheels. Three values were assigned to each parameter, and two wear states were considered for each type of wheel, one for new wheels and another one for reprofiled wheels. After processing the results of these simulations, it was concluded that all the parameters considered show very high influence, though the friction coefficient shows the highest influence. Therefore, it is recommended to undertake any future simulation job with measured track geometry and track irregularities, measured wheel profiles and normative values of the wheel–rail friction coefficient. [ABSTRACT FROM AUTHOR]

A sensitivity analysis has been performed to assess the influence of the elastic properties of railway vehicle suspensions on the vehicle dynamic behaviour. To do this, 144 dynamic simulations were performed modifying, one at a time, the stiffness and damping coefficients, of the primary and secondary suspensions. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy in future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the highest influences were found for the longitudinal stiffness and the lateral stiffness of the primary suspension, and the lowest influences for the vertical stiffness and the vertical damping of the primary suspension, with the parameters of the secondary suspension showing intermediate influences between them. [ABSTRACT FROM AUTHOR]

A sensitivity analysis has been performed to assess the influence of the inertial properties of railway vehicles on their dynamic behaviour. To do this, 216 dynamic simulations were performed modifying, one at a time, the masses, moments of inertia and heights of the centre of gravity of the carbody, the bogie and the wheelset. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy for future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the most sensitive inertial properties are the mass and the vertical moment of inertia, and the least sensitive ones the longitudinal and lateral moments of inertia. [ABSTRACT FROM AUTHOR]

In this paper, three numerical algorithms for the identification of wheel–rail contact forces based on measured wheel disc strains on an instrumented railway wheelset are discussed and compared. The three algorithms include one approach resting on static calibration, one that is applying a Kalman filter and the third is exploiting an inverse identification scheme. To demonstrate and evaluate the alternative methods, two load cases including periodic excitation by sinusoidal wheel–rail irregularities and transient excitation by an insulated rail joint are considered. Based on a previously presented vehicle–track interaction model in the time domain, load scenarios are defined by taking the calculated vertical wheel–rail contact forces as the reference force to be re-identified by the proposed algorithms. The reference contact forces are applied on a finite element model of the wheel to generate synthetic observation data, that is, radial strains at the positions of the strain gauges, serving as input to the identification procedures. It is concluded that the inverse identification scheme leads to superior accuracy at higher computational cost. If on-line implementation and evaluation is required, the Kalman filter generates better accuracy than the static calibration approach. [ABSTRACT FROM PUBLISHER]

Override simulations of two train units in frontal collision have been carried out using multi-body dynamics. The aim of this paper is to investigate the possible factors influencing the overriding behaviour throughout frontal collisions. In addition to the initial vertical offset defined in the standard EN 15227, the pitching motion of vehicles has a great effect on the overriding phenomenon. It depends on several factors, such as collision mass, pitching frequency, height of the centre of mass above the rail level. In this paper, it has been shown that the overriding phenomenon is more sensitive to variations in pitching frequency and height of the centre of mass, compared with the factor of the collision mass. Moreover, it has been demonstrated from simulation results that a 200-kN vertical force is required for the combined anti-climber devices (100 kN for each side anti-climber) to constrain the vertical relative motion between crashed train units. [ABSTRACT FROM AUTHOR]

Roadway departure while cornering constitutes a major part of car accidents and casualties in France. Even though drastic policy about overspeeding contributes to reduce accidents, there obviously exist other factors. This article presents the construction of a probabilistic strategy for the roadway departure risk assessment. A specific vehicle dynamic model is developed in which some parameters are modelled by random variables. These parameters are deduced from a sensitivity analysis to ensure an efficient representation of the inherent uncertainties of the system. Then, structural reliability methods are employed to assess the roadway departure risk in function of the initial conditions measured at the entrance of the curve. This study is conducted within the French national road safety project SARI that aims to implement a warning systems alerting the driver in case of dangerous situation. [ABSTRACT FROM AUTHOR]

The ride dynamic characteristics of a novel torsio-elastic suspension for off-road vehicle applications are investigated through field measurements and simulations. A prototype suspension was realised and integrated within the rear axle of a forestry skidder for field evaluations. Field measurements were performed on forestry terrains at a constant forward speed of 5 km/h under the loaded and unloaded conditions, and the ride responses were acquired in terms of accelerations along the vertical, lateral, roll, longitudinal and pitch axes. The measurements were also performed on a conventional skidder to investigate the relative ride performance potentials of the proposed suspension. The results revealed that the proposed suspension could yield significant reductions in magnitudes of transmitted vibration to the operator seat. Compared with the unsuspended vehicle, the prototype suspended vehicle resulted in nearly 35%, 43% and 57% reductions in the frequency-weighted rms accelerations along the x-, y- and z-axis, respectively. A 13-degree-of-freedom ride dynamic model of the vehicle with rear-axle torsio-elastic suspension was subsequently derived and validated in order to study the sensitivity of the ride responses to suspension parameters. Optimal suspension parameters were identified using the Pareto technique based on the genetic algorithm to obtain minimal un-weighted and frequency-weighted rms acceleration responses. The optimal solutions resulted in further reduction in the pitch acceleration in the order of 20%, while the reductions in roll and vertical accelerations ranged from 3.5 to 6%. [ABSTRACT FROM AUTHOR]

Driving simulation aims at reproducing, within a safe and controlled environment, sensorial stimuli as close to those perceived during the actual drive as possible, in order to induce driving behaviour similar to the real one. This paper illustrates an activity carried out on the driving simulator Virtual Environment for Road Safety, bound for system performance optimisation while dealing with subjective and objective tyres evaluation in the field of on-centre manoeuvres. Such activity can be divided into two main steps. The first one, described herewith, has been focusing on platform motion algorithms tuning and has led to driving simulator objective validation within the on-centre range. Device capability of reproducing dynamics, worked out by the vehicle model, has been thoroughly examined. Simulator sensitivity to a few tyre parameters influencing vehicle lateral dynamics has been analysed too. The second step - calling for the support of experienced drivers - will pursue subjective validation. [ABSTRACT FROM AUTHOR]

A combined lumped-parameter and multi-body system dynamic model of the human body-seat system has been constructed with masses and moments of inertia and with linear translational and rotational springs and dampers. The model was developed in four steps by minimising the sum-of-least-squares error between laboratory measurements and model predictions of the fore-and-aft driving point apparent mass and the fore-and-aft transmissibility of a car backrest. Good agreement was achieved between model predictions and both the median measured driving-point apparent mass and the median measured backrest transmissibility with six subjects. The model was capable of representing the measured apparent masses and predicting the backrest transmissibility with the individual subjects. It was also capable of predicting the backrest transmissibilities of two different car seats. A sensitivity study was conducted and the effects of the model parameters on the peak moduli and corresponding frequencies of the apparent mass and the backrest transmissibility are presented. [ABSTRACT FROM AUTHOR]

This paper introduces a risk assessment procedure for the crosswind stability of ground vehicles. A random variable gust model is combined with constrained simulation techniques and variance reducing Monte Carlo methods for an efficient computation of failure probabilities. Based on the failure probability, sensitivities, the influence of additional effects such as turbulence, track irregularities or the friction coefficient between wheel and road can be investigated on an objective basis. Moreover, the procedure allows us to compute the failure probabilities for vehicle journeys or a whole line. [ABSTRACT FROM AUTHOR]

This paper deals with the probabilistic investigation of the crosswind stability of ground vehicles with a strong focus on railway vehicle dynamics. The turbulent crosswind excitation is reduced to an artificial gust model, which is based on the so-called constrained simulation concept and where the gust amplitude, the gust duration and the aerodynamic coefficients of the vehicle are considered as random variables. The railway vehicle is simulated as a nonlinear multi-body vehicle model. Because of the random variables, a probabilistic analysis of the system has to be performed, including a reliability analysis to compute the overturning probability and including a sensitivity analysis concerning the random variables and the parameters of the probability density functions of the random variables. [ABSTRACT FROM AUTHOR]

This paper presents a design methodology for the mechanical systems entitled First Design. It is based on a hierarchical organisation of the design, taking into account the notion of robustness at an early phase of the project. The aim is to improve the quality of the system in order to make it robust, less sensitive to the variability of the external parameters and design parameters. We distinguish two main stages of the design cycle: one concerning functional parameters and another concerning physical parameters. The methodology is based on simplified models, on sensitivity analysis and on robust multi-objective optimisation. As an example, the methodology will be applied to the optimisation of vehicle suspension system design parameters. For each stage of the hierarchical design, adapted simplified models, sensitivity analyses and optimisation processes will be studied and applied to our vehicle suspension system. [ABSTRACT FROM AUTHOR]

We investigated the sensitivity of an observer based on a tire model using simulation in linear and nonlinear regions. In the linear region, we investigated the influence of vehicle speed by doing the same simulation at three speed levels. In the nonlinear region, the simulation condition was set such that the vehicle became unstable. In the linear region, steering input and cornering stiffness have a relatively large effect on the estimation error because these quantities determine tire side force. In the nonlinear region, the road surface’s friction coefficient becomes a crucial factor. In both the regions, the observer is sensitive to yaw rate and longitudinal speed. [ABSTRACT FROM AUTHOR]

The work described in this paper sets out to determine the optimal operating parameters for the dynamic interaction between the pantograph and the overhead for heavy haul train operations. The development of a measurement system that was used to determine and study important operating parameters is discussed. This lead to the development of an integrated three-dimensional simulation model. Data from on-track tests and that obtained from simulations show a good correlation. The model developed is representative of service conditions and includes different contact wire gradients, different span lengths as well as a bridge. A sensitivity analysis was done to evaluate the dynamic interactions due to changes in contact and catenary wire tensions, mean pantograph contact force as well as pantograph spacing in multiple locomotive consists. [ABSTRACT FROM AUTHOR]

The paper presents the results of analytical and simulation investigations on maximum possible truck velocity and lateral acceleration without rollover during curvilinear motion on an ideally smooth, horizontal, high friction road surface. Results of four different method were compared. 1st order sensitivity analysis was applied to investigate the influence of body CG height. [ABSTRACT FROM AUTHOR]