Modelling elastoplastic frictional collisions of ellipsoidal granules with collisional-SPH

The Collisional-SPH method models the combined evolution of deformation and frictional contact forces in elastoplastic granular collisions. However, there are many applications in which the granules are not spherical. In this paper, CSPH is extended to model an impact of an ellipsoidal granule on a flat deformable substrate. The CSPH spring-stiffness formulation is developed to account for the contact area eccentricity. Validation for different granule orientations and aspect-ratios are presented. The combined effect of substrate deformation and non-spherical granule shape on the contact-zone mechanics is investigated for different granule orientations and aspect ratios. It is found that the granule’s orientation and aspect ratio influences the interdependence between substrate deformation and contact-force distribution and should be accounted for in collision models.     

Toughness of the Pentagon Structure

On September 11, 2001, the reinforced concrete structure of the Pentagon Building was able to resist, without collapse, the impact of a large commercial airliner despite the total loss of 26 columns and severe damage to 15 columns at the ground level. The ensuing fire and related fire-fighting activities led to the collapse of a portion of the building approximately one-half hour after the impact. In this paper, the reasons for the demonstrated toughness of the reinforced concrete structure are examined and attributed to use of spiral columns, effective splicing of reinforcing bars, strong girders, and short span lengths.     

Modernization of the Driver Behaviour Questionnaire

IntroductionThe current study builds on previous versions of the Driver Behaviour Questionnaire (DBQ) by incorporating a larger sample of driving behaviors targeting inattention, distraction, aggressive driving, and health related to aging. The goals of this study were to determine if the resulting factor structure was consistent with a more contemporary view of unsafe driving behaviors, and to determine whether scores on the factors could predict self-reported collisions and police citations.MethodsThe instrument was given to a sample of 3295 drivers ranging in age from 19 to 80+ years old. It was divided in two sections, the first to provide demographic information and driving history data and the second containing 105 driver behavior questions.ResultsAn exploratory factor analysis resulted in a 65-item scale organized in four factors. The factors were labeled tentatively as Inattention Errors, Age-Related Problems, Distraction and Hurry, and Aggressive Violations. Regression analyses showed that the factors were predictors of self-reported, at-fault collisions and police citations.Practical implicationsThe factor scores found in this research are consistent with a useful theoretical framework for understanding unsafe driver actions, and demonstrate some potential to identify several individual difference variables that predict self-reported collisions and citations.     

Collisions and traffic violations of alcohol, cannabis and cocaine abuse clients before and after treatment

Prior research has shown that those with alcohol problems have significantly elevated rates of traffic events (i.e. traffic violations and collisions) than licensed drivers from the general population and that treatment is associated with reductions in alcohol-related collisions. However, very little research exists on traffic events and the impact of treatment for cannabis or cocaine clients. The objectives of this research are: (1) to determine whether clients in treatment for a primary problem of alcohol, cannabis or cocaine have significantly elevated rates of traffic events than a matched control group of licensed drivers; and (2) to assess whether a significant reduction in traffic events occurs after treatment for each client group compared to a control group. Driver records of patients admitted to substance abuse treatment in 1994 for a primary problem of alcohol (n = 117), cannabis (n = 80) or cocaine (n = 169) were accessed from the Ministry of Transportation for Ontario, Canada. A comparison group of 504 licensed drivers frequency matched by age, sex and place of residence, was also randomly selected. Data was collapsed into two 6-year time periods: 1988-1993 (i.e. before treatment) and 1995-2000 (i.e. after treatment). Six repeated measures analysis of variance tests were conducted where traffic violations and collisions of three treatment groups (i.e. alcohol, cannabis or cocaine) and a control group were compared before and after treatment. All three treatment groups had significantly more traffic violations than the control group and no significant interactions between time period and group membership were found. For collisions, there was a significant interaction between the alcohol and control groups and between the cocaine and control groups. The average number of collisions for the alcohol and cocaine groups decreased after completing treatment, whereas the number for the control group was stable over the same time periods. Neither the interaction term nor the between group effect was significant in the comparison of the cannabis and control groups. When rates of collisions were calculated based on the period that each driver had a valid license, the interaction term was still significant for the comparison of the alcohol and control groups but not for the cocaine and control groups. The results contribute to existing literature by demonstrating that cocaine and cannabis clients have a higher risk of traffic violations than matched controls and that reductions in collision risk was found after treatment for the alcohol and cocaine groups. More research is needed to better understand the reasons for the higher risk of traffic events and to determine reasons for declines.     

A study on tangential force laws applicable to the discrete element method (DEM) for materials with viscoelastic or plastic behavior

The discrete element method is a widely used particle orientated simulation approach for modeling granular systems. It is based on tracking each particle's movement and its interactions with the surroundings over time. The motion of a particle is given by a system of coupled ordinary differential equations which are solved numerically. Therefore, models for the forces acting between particles in contact need to be specified. In the past, detailed investigations dealing with the accuracy of tangential force-displacement models have been very limited, with sparse experimental data considered and the frequent restriction of including only fully elastic materials. In large scale discrete element simulations, on the other hand, viscoelastic or plastic material behavior is often assumed for normal contacts and combined with arbitrary tangential models. To address this situation a number of tangential force-displacement models are reviewed including linear models by Cundall and Strack [1979. A discrete numerical model for granular assemblies, Geotechnique 29, 47-65], Di Maio and Di Renzo [2004. Analytical solution for the problem of frictional-elastic collisions of spherical particles using the linear model. Chemical Engineering Science 59(16), 3461-3475], Brendel and Dippel [1998. Lasting contacts in molecular dynamics simulations. In: Herrmann, H.J., Hovi, J.-P., Luding, S. (Eds.), Physics of Dry Granular Media, Dordrecht. Kluwer Academic Publishers, pp. 313], Walton and Braun [1986. Viscosity, granular temperature and stress calculations for shearing assemblies of inelastic, frictional disks. Journal of Rheology 30, 949] and simple non-linear models by Brilliantov et al. [1996. Model for collisions in granular gases. Physical Review E 53(5), 5382-5392], Tsuji et al. [1992. Lagrangian numerical simulation of plug flow of cohesionless particles in a horizontal pipe. Powder Technology 71, 239-250] and Di Renzo and Di Maio [2005. An improved integral non-linear model for the contact of particles in distinct element simulations. Chemical Engineering Science 60(5), 1303-1312]. Whereas for fully elastic materials the parameters of the tangential force-displacement models can be derived directly from mechanical properties a scaling approach is proposed for the estimation of the parameters in the non-elastic case. The effect of different normal force-displacement models is analyzed. For all model combinations macroscopic final collision properties are derived and compared to experimental results by Foerster et al. [1994. Measurements of the collision properties of small spheres. Physics of Fluids 6(3), 1108-1115], Lorenz et al. [1997. Measurements of impact properties of small, nearly spherical particles. Experimental Mechanics 37(3), 292-298], Gorham and Kharaz [2000. The measurement of particle rebound characteristics. Powder Technology 112(3), 193-202] and Dong and Moys [2003. Measurement of impact behaviour between balls and walls in grinding mills. Minerals Engineering 16(6), 543-550; 2006. Experimental study of oblique impacts with initial spin. Powder Technology 161(1), 22-31].     

Grid emulation for managing random sensor networks

A common assumption in sensor networks is that sensors are located according to a uniform random distribution. In this paper, we show that uniform random points on the two dimensional unit square are almost a “grid”. In particular, for a synchronous geographic sensor network we show how to emulate any grid protocol on random sensor networks, with high probability.This suggests the following framework. In order to solve a problem on a random sensor network, we solve the same problem on a grid. Then we use our emulation to make the obtained solution suitable for random sensor network. We analyze the cost of the emulation in terms of consumed energy and time. Finally, we provide some examples that illustrate our method.     

Effects of roadside memorials on traffic flow

Despite their growing popularity in North America, little research has been conducted on understanding the effects of roadside memorials on drivers’ behaviour. In this study, we examined the short-term effects of roadside memorials on traffic speed and headways on a high speed intercity freeway as well as its long-term effect on traffic speed on a high speed urban freeway. Our study found that the placement of roadside memorials did not have any significant effect on traffic speeds or headways, either in the short or long term. Therefore, concerns about the negative effects on driver behaviour were not supported by this research, at least with regards to speeding and following too closely. However, no positive effects on safety were found either.     

Structure,nonlinearity, and system theory

The suggestion of writing, for some problems, nonlinear state equations not as dx/dt = F(x,u,t), but as dx/dt = [A(t,x)]x + [B(t,x)]u(t), which is more ‘constructive’ as re system perception and possible structural generalizations, is considered, supported by arguments related to the classification of switched circuits as linear and nonlinear. The point of the distinction is mainly that when solving dx/dt = F(x,u,t), one immediately dwells into the analytical problems related to pure mathematics, whereas for dx/dt = [A(t,x)]x + [B(t,x)]u(t), considering first a constant matrix [A], one introduces the system's physical structure and considering then [A(x)] sees the nonlinearity of the system as a dependence of the structure on the processes in it or on system's input. (This might be named structural response). The thinking in terms of structure better observes the engineering and physical degrees of freedom, which are relevant regarding applications. Some electronic systems and physical systems (e.g., hydrodynamic) are considered in these terms. The logical side is always the focus, and the pedagogical (even philosophical) side is not ignored. Copyright © 2013 John Wiley & Sons, Ltd.     

Road safety impact of extended drinking hours in Ontario

PURPOSE: On 1 May 1996, Ontario, Canada amended the Liquor Licence Act to extend the hours of alcohol sales and service in licensed establishments from 1 to 2 a.m. The purpose of this study was to evaluate the road safety impact of extended drinking hours in Ontario. METHOD: A quasi-experimental design using interrupted time series with a nonequivalent no-intervention control group was used to assess changes. The analyzed data sets are total and alcohol-related, monthly, traffic fatalities for Ontario, for the 11-12 p.m., 12-1 a.m., 1-2 a.m. and 2-3 a.m. time windows, for Sunday through Wednesday nights and for Thursday through Saturday nights, for 4 years pre- and 3 years post-policy change, compared to neighbouring regions of New York and Michigan. RESULTS: The blood alcohol concentration positive driver fatality trends reflected downward trends for Sunday-Wednesday 12-2 a.m. and Thursday-Saturday 1-2 a.m. for Ontario and downward trends for Thursday-Saturday 12-1 a.m. and 2-3 a.m. for New York and Michigan after the extended drinking hour policy change. Ontario total fatality data showed similar trends to the Ontario blood alcohol positive trends. CONCLUSIONS: The multiple datasets converge in suggesting little impact on BAC positive fatalities with extension of the closing hours. These observations are consistent with other studies of small changes in alcohol availability.     

Building as Interface: or,What Architects Can Learn from Interaction Designers

Walter Aprile and Stefano Mirti have been engaged as designers, researchers and teachers at Interaction-Ivrea, a technological research institute in northern Italy, since it was established by Telecom Italia and Olivetti in 2001. Here, the two reflect on the series of experiments they have undertaken at the intersection of interactive technology and architecture, analysing their own working systems and the means by which they have chosen to pursue interdisciplinary dialogue. Copyright © 2005 John Wiley & Sons, Ltd.