Absorbed power of small children

Objective. To experimentally measure the seated vertical direction whole-body absorbed power characteristics of small children less than 18 kg in mass. Background. Several studies have reported whole-body absorbed power for adult humans, but no data has been published previously for small children. Methods. Eight children were tested in a laboratory test rig which incorporated safety features which satisfy existing international standards for human testing. Force and acceleration were measured at the point of input to a rigid seat at a sampling rate of 200 Hz, and analysis was performed over the interval from 1.0 to 45.0 Hz. A double normalised (both input acceleration and test subject mass) measure of absorbed power was used. Results. The vertical whole-body power absorption characteristics of the small children were found to present differences with respect to those of adults. The mean frequency of peak absorption was found to be 7.4 Hz as opposed to approximately 4.0–5.0 for adults. The interval of absorption was found to be from approximately 3 to 16 Hz and the total double normalised absorbed power was found to be 86% that of adults. Conclusions. The differences in dynamic response between small children and adults raise questions regarding the applicability of whole-body vibration guidelines such as ISO-2631 in the case of small children since these guidelines were developed from mechanical and subjective response data of adults

In-vehicle vibration study of child safety seats

This paper reports experimental measurements of the in-vehicle vibrational behaviour of stage 0&1 child safety seats. Road tests were performed for eight combinations of child, child seat and automobile. Four accelerometers were installed in the vehicles and orientated to measure as closely as possible in the vertical direction; two were attached to the floor and two located at the human interfaces. An SAE pad was placed under the ischial tuberosities of the driver at the seat cushion and a child pad, designed for the purpose of this study, was placed under the child. 4 test runs were made over a pave’ (cobblestone) surface for the driver’s seat and 4 for the child seat at both 20 km/h and 40 km/h. Power spectral densities were determined for all measurement points and acceleration transmissibility functions (ATFs) were estimated from the floor of the vehicle to the human interfaces. The system composed of automobile seat, child seat and child was found to transmit greater vibration than the system composed of automobile seat and driver. The ensemble mean transmissibility in the frequency range from 1 to 60 Hz was found to be 77% for the child seat systems as opposed to 61% for the driver’s seats. The acceleration transmissibility for the child seat system was found to be higher than that of the driver’s seat at most frequencies above 10 Hz for all eight systems tested. The measured ATFs suggest that the principal whole-body vibration resonance of the children occurred at a mean frequency of 8.5, rather than the 3.5 to 5.0 Hz typically found in the case of seated adults. It can be concluded that current belt-fastened child seats are less effective than the vehicle primary seating systems in attenuating vibrational disturbances. The results also suggest the potential inability of evaluating child comfort by means of existing whole-body vibration standards

Facilitating the driver detection of road surface type by selective manipulation of the steering-wheel acceleration signal

Copyright @ 2012 by Institution of Mechanical Engineers.Previous research has investigated the possibility of facilitating the driver detection of road surface type by means of selective manipulation of the steering-wheel acceleration signal. In previous studies a selective increase in acceleration amplitude has been found to facilitate road-surface-type detection, as has selective manipulation of the individual transient events which are present in the signal. The previous research results have been collected into a first guideline for the optimization of the steering-wheel acceleration signal, and the guideline has been tested in the current study. The test stimuli used in the current study were ten steering-wheel acceleration-time histories which were selected from an extensive database of road test measurements performed by the research group. The time histories, which were all from midsized European automobiles and European roads, were selected such that the widest possible operating envelope could be achieved in terms of the r.m.s. value of the steering acceleration, the kurtosis, the power spectral density function, and the number of transient events present in the signal. The time histories were manipulated by means of the mildly non-stationary mission synthesis algorithm in order to increase, by a factor of 2, both the number and the size of the transient events contained within the frequency interval from 20 Hz to 60Hz. The ensemble, composed of both the unmanipulated and the manipulated time histories, was used to perform a laboratory-based detection task with 15 participants, who were presented the individual stimuli in random order. The participants were asked to state, by answering 'yes' or 'no', whether each stimulus was considered to be from the road surface that was displayed in front of them by means of a large photograph on a board. The results suggest that the selectively manipulated steering-wheel acceleration stimuli produced improved detection for eight of the ten road surface types which were tested, with a maximum improvement of 14 per cent in the case of the broken road surface. The selective manipulation did lead, however, to some degradation in detection for the motorway road stimulus and for the noise road stimulus, thus suggesting that the current guideline is not universally optimal for all road surfaces

Apparent mass of small children: Modelling

Mass-spring-damper models are widely available for quantifying the whole-body vibration characteristics of primates, human adolescents and human adults, but no models have previously been developed for small children. In this study a single degree of freedom, linear, mass-spring-damper with base support model was determined from the seated vertical apparent mass modulus function of each of eight small children of less than 18 kg in mass. A Differential Evolution optimisation algorithm was used in conjunction with a mean squared error measure and penalty functions to identify the optimal child model parameter values. The eight child models were characterised by a mean moving mass m1 of 8.5 kg, a mean body stiffness k1 of 21131 N/m and a mean damping coefficient c1 of 329 Ns/m. Comparison to the parameter values of similar models reported in the literature for Rhesus monkeys, Baboons, large children and adults suggests that the values obtained in the current study for small children are intermediate between the smaller primates and the larger humans. A regression analysis of the model parameters was performed as a function of subject mass for a data set consisting of the eight child models, twelve similar models for primates, and 60 similar models for large children and adults. The moving mass m1 of the group of models grew with a power exponent of approximately unity, the body stiffness k1 grew with a power exponent of approximately +1/2, the damping coefficient c1 grew with a power exponent of approximately +3/4 and the dimensionless damping ratio was independent of subject mass. The natural frequency of the models grew with a power exponent of approximately –1/4

Perception enhancement for steer-by-wire systems

Modern automobiles are safer and more comfortable than ever before. If there is one criticism that can be made, however, it is that the achievement of higher levels of comfort has sometimes come at the expense of a lack of driver involvement. The issue of driver involvement can become critical in the case of by-wire systems since these systems do not necessarily have a predetermined path or transfer mechanism for carrying stimuli to the driver. This article discusses the technical requirements of perception enhancing systems for the vehicle steering

Renewal sequences, disordered potentials, and pinning phenomena

We give an overview of the state of the art of the analysis of disordered models of pinning on a defect line. This class of models includes a number of well known and much studied systems (like polymer pinning on a defect line, wetting of interfaces on a disordered substrate and the Poland-Scheraga model of DNA denaturation). A remarkable aspect is that, in absence of disorder, all the models in this class are exactly solvable and they display a localization-delocalization transition that one understands in full detail. Moreover the behavior of such systems near criticality is controlled by a parameter and one observes, by tuning the parameter, the full spectrum of critical behaviors, ranging from first order to infinite order transitions. This is therefore an ideal set-up in which to address the question of the effect of disorder on the phase transition,notably on critical properties. We will review recent results that show that the physical prediction that goes under the name of Harris criterion is indeed fully correct for pinning models. Beyond summarizing the results, we will sketch most of the arguments of proof.Comment: 32 pages. Notes from lectures given at the summer school on Spin Glasses (June 25- July 6, 2007). Birkhauser, eds. A. Boutet de Monvel and A. Bovier (to appear

Self-Reported Upper Body Discomfort due to Driving: Effect of Driving Experience, Gender and Automobile Age

This study investigated the human upper body discomfort caused by automobile driving. Both global and local discomfort estimates were achieved by means of a self-administered questionnaire. The questionnaire used a Borg CR10 scale to evaluate human discomfort, and contained sections to gather information regarding the driving experience, gender and most frequently used automobile of the respondent. The geographic area surveyed was the city of Turin, Italy, and data from a total of 269 drivers was analysed. For all subgroups analysed, the back region was reported to suffer the greatest discomfort, followed in order of decreasing discomfort by the neck, shoulder, arm, hand-wrist, forearm, head, chest and mandible. Generally, female drivers provided higher discomfort responses than male drivers. Subdividing the data according to driving experience lead to large and statistically significant (a<0.05) differences inboth global and local discomfort. Subdividing by gender suggested some significant differences, while subdividing by automobile age produced few differences. The results suggest the usefulness of controlling for test subject driving experience and gender when performing subjective evaluations of automobiles. Further, comparison of the global and the local discomfort responses suggested that individuals were able to form a stable estimate of global discomfort based on the sensations perceived in each of the individual body regions involved. This suggests the interesting possibility that global evaluations may not always provide an accurate understanding of human discomfort since situations can be imagined in which different distributions of upper body discomfort might produce the same, global, response

Renewal convergence rates and correlation decay for homogeneous pinning models

A class of discrete renewal processes with super-exponentially decaying inter-arrival distributions coincides with the infinite volume limit of general homogeneous pinning models in their localized phase. Pinning models are statistical mechanics systems to which a lot of attention has been devoted both for their relevance for applications and because they are solvable models exhibiting a non-trivial phase transition. The spatial decay of correlations in these systems is directly mapped to the speed of convergence to equilibrium for the associated renewal processes. We show that close to criticality, under general assumptions, the correlation decay rate, or the renewal convergence rate, coincides with the inter-arrival decay rate. We also show that, in general, this is false away from criticality. Under a stronger assumption on the inter-arrival distribution we establish a local limit theorem, capturing thus the sharp asymptotic behavior of correlations.Comment: 13 page

On the localized phase of a copolymer in an emulsion: supercritical percolation regime

In this paper we study a two-dimensional directed self-avoiding walk model of a random copolymer in a random emulsion. The copolymer is a random concatenation of monomers of two types, $A$ and $B$, each occurring with density 1/2. The emulsion is a random mixture of liquids of two types, $A$ and $B$, organised in large square blocks occurring with density $p$ and $1-p$, respectively, where $p \in (0,1)$. The copolymer in the emulsion has an energy that is minus $\alpha$ times the number of $AA$-matches minus $\beta$ times the number of $BB$-matches, where without loss of generality the interaction parameters can be taken from the cone $\{(\alpha,\beta)\in\R^2\colon \alpha\geq |\beta|\}$. To make the model mathematically tractable, we assume that the copolymer is directed and can only enter and exit a pair of neighbouring blocks at diagonally opposite corners. In \cite{dHW06}, it was found that in the supercritical percolation regime $p \geq p_c$, with $p_c$ the critical probability for directed bond percolation on the square lattice, the free energy has a phase transition along a curve in the cone that is independent of $p$. At this critical curve, there is a transition from a phase where the copolymer is fully delocalized into the $A$-blocks to a phase where it is partially localized near the $AB$-interface. In the present paper we prove three theorems that complete the analysis of the phase diagram : (1) the critical curve is strictly increasing; (2) the phase transition is second order; (3) the free energy is infinitely differentiable throughout the partially localized phase.Comment: 43 pages and 10 figure