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This paper presents a new structural bump foil model that can handle all operating conditions from start-up to full speed. The model is based on a nonlinear contact algorithm with friction and gaps. The top foil is modeled as a curved beam while bump foil uses a coupled truss model. The model considers the gaps between the bump foil and the bearing casing, between the bump foil and the top foil and between the rotor and the top foil. Thus, any numerical interference between the rotor and the top foil is avoided. A mixed lubrication model is used for the thin film pressures. Following this algorithm, contact pressures appear if the film thickness is less than three times the equivalent roughness of the rotor and of the top foil. Fluid pressures are calculated from numerical solutions of Reynolds equation while contact pressures, if present, are calculated with the model of Greenwood and Williamson. The model is validated by comparisons with the experimental results obtained for start-up operating conditions of a first-generation foil bearing of 38.1 mm diameter with static loads of 10–50 N. Theoretical predictions of the start-up torque and takeoff speed compare well with experimental results. It is also shown how manufacturing bump height errors can explain the differences between theoretical and experimental predictions. Further validations are presented for the same bearing operating at high speeds (30, 45, and 55 krpm) and heavy static loads (up to 200 N). The calculated minimum film thickness and attitude angle are compared with experimental data from the literature.

An experiment was designed and carried out to study the friction and deformation of carbon fibre tow under sliding transverse to the orientation of the fibres. A continuous frictional force was measured in reciprocal sliding tests over a sliding length of about one width of the tow, using incremental tests of 4 mm of sliding with a stop after each millimetre to measure the topography of the tow in contact with a glass plate. Although the friction coefficient depended on the initial state of the tow in the first millimetres of sliding, this effect tended to disappear with sliding distance under both dry and epoxylubricated conditions. Four stages of friction were identified and related to their underlying mechanisms: internal stress relaxation, shear deformation of the tow and microslips at the interfaces, macroslip of the external interfaces, and force relaxation after the end of glass sliding.

AimsThis study aims to assess the stigmatization of Moroccans towards substance and nonsubstance addictions, as well as to explore its relationship with both demographic factors and addiction familiarity.Methods527 Moroccans anonymously participated in a cross-sectional study via an online survey that was distributed on social media. Participants were randomly assigned 2 vignettes describing either substance (Alcohol and Cannabis) or non-substance (Gambling and Social Media) addictions, followed by the Social Distance Scale and the Familiarity Scale.ResultsA total of 527 individuals answered our online questionnaire. The median age of respondents was 27.6 years (std = 15.66). 56% were females and 44% were males. Among the participants 45% were married and 50% were medical students or health professionals.Using ANOVA and a series of student t-tests, that yielded a p < 0.05, the following results were obtained:A moderate level of stigma was found towards all addictions, except for social media where no stigma was found (p < 0.05). In contrast, the familiarity level was high with social media addiction and low with the other addictions (p < 0.05).The women in our study showed higher stigmatization of all addictions, whereas older people (>43 years) showed higher stigmatization of substance addictions only.Different levels of stigmatization were observed towards the 4 types of addiction; the highest being cannabis addiction and the lowest being social media addiction.Regarding familiarity with addiction, males were more familiar with all types of addiction. Whereas, younger individuals (<23 years) were the least familiar with substance addiction.Moroccans’ familiarity levels with different types of addiction were significantly different. Familiarity with social media addiction was the highest whereas familiarity with gambling addiction was the lowest.Using the Pearson correlation, we found that stigma and familiarity concerning substance addiction were negatively correlated (r=−0,30, p < 0.01). A stronger, yet moderate relationship was found between stigma and familiarity regarding cannabis (r=−0,36, p < 0.01).ConclusionIt seems that Moroccans stigmatize against most addictions, which was found to be influenced by multiple factors including familiarity level, age, and sex. These findings can be used as a base to create a targeted educational campaign to tackle addiction in our society. No significant conclusions were made concerning whether or not the academic level or the health professional background influenced stigmatization, which raises concerns about the Moroccan academic and medical curricula's representation of addiction.

The present work presents the numerical investigation of the bump height manufacturing errors on the unbalance response of an aerodynamic foil journal bearing. This is the first study of the impact of manufacturing errors based on an important number of samples. A statistical analysis predicts the mean values of the characteristics and the standard errors of the mean. The paper presents the most important aspects of the numerical model that was used and the way it was implemented for the unbalance analysis of a four degrees of freedom rotor. It was considered that the bump height manufacturing errors had a normal distribution (i.e. each bump had a different random height) around the design (mean) height value. The standard deviation of the bump heights (the same for all bumps) is a measure of the magnitude of the manufacturing errors. The results give a qualitative but above all quantitative overview of the impact of machining errors on some characteristics of aerodynamic foil bearings.

This experimental work focuses on the evaluation of deformation mechanisms due to sliding between carbon fiber tows with a flat tool in dry and lubricated with liquid resin conditions. The experiments were carried out on manually woven and single tows. The effect of angle between tow axes and sliding direction was also studied. The topography of the tows in contact with a sliding transparent glass plate was measured with a 3D optical microscope before and after sliding. These measurements revealed a decrease of roughness with sliding in all tested conditions, a contraction of lubricated single tows in perpendicular to sliding orientation, and high residual displacements in lubricated woven tows in 0°/90° orientation and dry single tows in perpendicular to sliding orientation.

The paper presents a new structural bump foil model that can handle all operating conditions from start-up to full speed. The model is based on a non-linear contact algorithm with friction and gaps. The top foil is modeled as a curved beam while bump foil uses a coupled truss model. The model considers the gaps between the bump foil and the bearing casing, between the bump foil and the top foil and between the rotor and the top foil. Thus, any numerical interference between the rotor and the top foil is avoided. A mixed lubrication model is used for the thin film pressures. Following this algorithm, contact pressures appear if the film thickness is less than three times the equivalent roughness of the rotor and of the top foil. Fluid pressures are calculated from numerical solutions of Reynolds equation while contact pressures, if present, are calculated with the model of Greenwood and Williamson. The model is validated by comparisons with the experimental results obtained for start-up operating conditions of a first generation foil bearing of 38.1 mm diameter with static loads of 10 N to 50 N. Theoretical predictions of the start-up torque and take-off speed compare well with experimental results. It is also shown how manufacturing bump height errors can explain the differences between theoretical and experimental predictions. Further validations are presented for the same bearing operating at high speeds (30, 45 and 55 krpm) and heavy static loads (up to 200 N). The calculated minimum film thickness and attitude angle are compared with experimental data from the literature.