Enhanced friction modeling for steady-state rolling tires

Tire modeling is nowadays a necessary tool in the tire industry. Car manufacturers, governments and consumers demand better traction under all circumstances, less wear and more recently less noise and a lower rolling resistance. Therefore finite element analysis is adopted in the design process of new tires to cope with these, often conflicting, demands. Finite element tire modeling can increase the insight on specific properties of a tire, decrease the development time and reduce development costs of new tires. However in practice most finite element models are still not able to match outdoor experiments. Both the static deformation and the dynamic response of the tire rolling on the road should be accurately predicted. The cornering, braking and traction of a tire depend on the generated friction forces. Friction depends not only on the tread properties of the tire, but also on the road surface and environmental conditions. The main goal of this thesis is to develop a robust and numerically efficient friction model for finite element tire simulations and to create a framework for the identification and implementation of friction related parameters. The numerical modeling of a tire in combination with its environment is a challenging task, since different physical phenomena play a role. Typically the techanical, thermal and fluid domains contribute to the tire response. This research is restricted to the mechanical domain, where a numerical modeling framework for steady-state rolling tire simulations is defined. In future developments of the model other effects can be included using this framework as a base. One of the objectives of this thesis is to develop and validate a tire friction model for finite element analysis, which captures observed effects of dry friction on the handling characteristics of rolling tires. Friction by itself is a highly complex interaction phenomenon between contacting materials and can be modeled on many different length scales, applying different numerical techniques. This can however lead to an enormous computational burden and as a result it can be impractical for an industrial application. To provide a numerically feasible and relatively fast solution a phenomenological friction model is chosen, where the parameters are identified using a two step experimental / numerical approach. Firstly, friction experiments are performed on a laboratory abrasion and skid tester to investigate the influence of contact pressure on the frictional force. In this experimental setup a small solid tire, with adjustable side slip angle, is pressed on an abrasive disk. The friction present between the abrasive disk and solid tire drives the tire and the resulting forces are measured with a force sensor. Several experiments under different normal loads and side slip angles of the tire are conducted. These measurements, under low rolling velocity, are used to identify contact pressure dependent friction parameters. The relevant parts of this setup are modeled in the commercial finite element package ABAQUS and the steady-state performance of the small tire under different slip angles is evaluated and compared with experiments. It is shown that the present turn slip, which has great impact on the slip velocity field at the trailing edge of the contact area, is captured well with the model. Furthermore, the calculated cornering stiffness is in good agreement with the experiments. Secondly, outdoor braking experiments at different velocities with a full scale tire are conducted to obtain a velocity dependent parameter set for the tire friction model. The derived friction model is then coupled to a finite element model of this full scale tire, which is also constructed in the software package ABAQUS. The finite element model is validated statically using measurements of the contact pressure distribution, contact area and of the radial and axial stiffness of the tire. The steady-state transport approach in ABAQUS is used to efficiently compute steady-state solutions at different forward velocities as used in the outdoor experiments. Finally, the predictive capability of the FE tire model in combination with the proposed friction model is assessed. The basic handling characteristics, such as pure braking, pure cornering, and combined slip under different loads, inflation pressures and velocities are evaluated and validated with experiments. Based on this comparison, it can be concluded that all three basic handling characteristics are adequately predicted

Visualizing individual dynamics:The case of a talented adolescent

Research on talent and performance development has primarily focused on inter-individual differences. However, research suggests that performance and the underlying determinants change over time, in an individual-specific dynamic way. This chapter illustrates a method to measure, understand, and visualize the performance- and psychosocial dynamics of a talented adolescent athlete. During one season, a talented tennis player filled out an online diary questionnaire twice a week. We visualized the results using R-scripts that we made openly available. This facilitated the interpretation of the athlete’s performance- and psychosocial dynamics, which are influenced by particular events in the athlete’s life. Altogether, the current study provides insight into how the adolescent and the context interact and mutually affect each other in successive iterations

Напрями та шляхи вдосконалення матеріально-технічного забезпечення підприємств АПК регіону

Background The growing number of web-based psychological treatments, based on textual communication, generates a wealth of data that can contribute to knowledge of online and face-to-face treatments. We investigated whether clients language use predicted treatment outcomes and adherence in Master Your Mood (MYM), an online group course for young adults with depressive symptoms. Methods Among 234 participants from a randomised controlled trial of MYM, we tested whether their word use on course application forms predicted baseline levels of depression, anxiety and mastery, or subsequent treatment adherence. We then analysed chat session transcripts of course completers (n=67) to investigate whether word use changes predicted changes in treatment outcomes. Results Depression improvement was predicted by increasing use of 'discrepancy words' during treatment (e.g. should). At baseline, more discrepancy words predicted higher mastery level. Adherence was predicted by more words used at application, more social words and fewer discrepancy words. Limitations Many variables were included, increasing the chance of coincidental results. This risk was constrained by examining only those word categories that have been investigated in relation to depression or adherence. Conclusions This is the first study to link word use during treatment to outcomes of treatment that has proven to be effective in an RCT. The results suggest that paying attention to the length of problem articulation at application and to 'discrepancy words' may be wise, as these seem to be psychological markers. To expand knowledge of word use as psychological marker, research on web-based treatment should include text analysis. © 2014 The Authors

A Cross-Cultural Study of Physician Treatment Decisions for Demented Nursing Home Patients Who Develop Pneumonia

PURPOSE We wanted to explore factors that influence Dutch and US physician treatment decisions when nursing home patients with dementia become acutely ill with pneumonia