CM Labs Simulations (Canada)

Modeling multibody systems subject to unilateral contacts and friction efficiently is challenging, and dynamic formulations based on the mixed linear complementarity problem (MLCP) are commonly used for this purpose. The accuracy of the MLCP solution method can be evaluated by determining the error introduced by it. In this paper, we find that commonly used MLCP error measures suffer from unit inconsistency leading to the error lacking any physical meaning. We propose a unit-consistent error measure, which computes energy error components for each constraint dependent on the inverse effective mass and compliance. It is shown by means of a simple example that the unit consistency issue does not occur using this proposed error measure. Simulation results confirm that the error decreases with convergence toward the solution. If a pivoting algorithm does not find a solution of the MLCP due to an iteration limit, e.g., in real-time simulations, choosing the result with the least error can reduce the risk of simulation instabilities and deviation from the reference trajectory.

As part of the Dutch post-license young driver coaching program, Drive Xperience (DX), the level of moral reasoning was explored in relation to self-reported violating driving behaviors. Drawing from literature in the field of juvenile crime, three online assessments were developed to measure: a) social driving behavior; b) moral justification for rule compliance, and: c) cognitive distortions in relation to socially undesirable driving behavior. The assessments were administered between fall 2014 and fall 2016 to1660 participants in the DXprogram. The results show that immature levels of moral reasoning and prevalence of cognitive distortions are strongly associated with self-reported speed choice, space competition and traffic law violations.

Underdeveloped hazard perception skills are associated with the higher crash risk of young novice drivers. Some driver licensing authorities use hazard perception tests (HPTs) that measure reaction times or multiple-choice responses to brief driving scenes videotaped from a vehicle traveling at legal speeds. To date, evaluations of the association between HPT scores and novice driver crash rates have been mixed. Several possible explanations for this are: high-risk novice drivers may offset good HP skills by exceeding the speed limit; current HPTs do not capture behavioral responses to hazards from candidates whose attention is engaged in the driving task; there is no established typology of driving hazards that might produce a finer-grained analysis of test results, and; current measures of HP ability may lack sensitivity. To address these potential flaws, the authors developed a driving simulator-based Hazard Response Test (HRT) in which drivers respond to sixteen programmed hazard events derived from a proposed typology that combines visible or hidden, real or potential conflicts, while driving over three continuous routes. The study results indicate no statistically significant difference in crash rates between young novice and experienced drivers. However, a novel, composite measure called the Continuous Time to Collision (C-TTC) did discriminate between young novice and older experienced drivers. Additional research on the validation of this measure and further refinement of the hazard typology could contribute to the creation of a standardized, driving simulator-based HRT for use in the evaluation of novice, professional and aging drivers.

A new framework is developed in this paper for the efficient implementation of semi-empirical terramechanics models in multibody dynamics environments. In this approach, for every wheel in contact with soft soil, unilateral contact constraints are added to the solver in both the normal direction and the tangent plane. The forces associated with the tangent plane, like traction and rolling resistance, are formulated in this approach as set-valued functions, whose properties are determined by deregularization of the above-mentioned terramechanics relations. As shown in this paper, this leads to the dynamics representation in the form of a linear complementarity problem (LCP). With this formulation, stable simulation of rovers is achieved even with relatively large time steps. In addition, a high-resolution height-field is employed to model terrain-surface deformations and changes in hardening of soil under the wheel. As a result, the multi-pass effect is also captured in our approach. In addition, an extensive set of experiments was conducted using a version of the Juno rover (Juno II). The experimental results are analyzed and compared with the model developed in the paper.

In this work, we investigate the effect of terrain modelling on the performance of planetary rovers by evaluating various design concepts under typical rover manoeuvres. The analysis is based on implementations in CMLabs’ Vortex, a dynamics simulation environment for complex mechanical systems. Vortex can be used to model the contact of wheels under various terrain conditions. The particular focus is on motion on soft terrain, investigating the physical phenomena exhibited by such terrain, and the possibility of modelling these with the primary purpose of representing the effects of the terrain on rover behaviour. Two semi-empirical terramechanics models are used to represent the effect of soft soil. The implementation of these terramechanics models in Vortex and their adaptation to fit a multibody dynamics simulation environment are explained in detail. The effects of terrain modelling approaches on the performance of rover concepts under typical rover manoeuvres are investigated. These include: (i) stra...

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