Car seat and occupant modelling using CAD

A current Brite-Euram project is concerned with life-cycle aspects of car seating with Loughborough being responsible for driver comfort assessment. This is being carried out through road and laboratory trials, with the results to be incorporated within the SAMMIE design system. Driver comfort is in part determined by seat pressure distributions which lead to deformation of the human flesh and the seat and movement of important design locations such as the driver's eyepoint. Accommodation of these effects requires a more realistic representation of the human body using surface rather than solid representations. Hence a shadow scanning technique is used to capture human body shape which is processed into the DUCT surface modelling system and via IGES files into SAMMIE. Finite element techniques are then used to predict deformations at the seat/driver interface

Computer aided modelling of the human spine

The human spine is the main structure to support human body weight and external loads, to allow the torso to reach to a variety of positions and to protect the spinal nervous system. Lumbar back pain and disorders may be related to spinal curvature and disc pressure, and it is an ultimate objective of the work reported here to include consideration of these issues in computer aided ergonomics design systems for evaluating a wide range of situations including manual handling and car seat design. Several methods from structural analysis have previously been used to model the human spine, principally lever and beam structures, but these have frequently shown discrepancies when compared with experimental data. As an alternative, an arch representation for the spine is considered here and allows the establishment of a criterion for the failure of the spine that may be useful in determining absolute maximum loading conditions. However, the main interest is in submaximal loading conditions where damage or discomfort are the concerns rather than fracture. It is proposed that the location of the thrust line in relation to the centre-line of the spine is a useful predictor, and optimization techniques have been developed to find the ‘best-fitting’ thrust line for the statically indeterminate structure. Further work is concerned with adding muscle and ligament forces to the loading system of the model, extension of the two-dimensional model into three dimensions, validation against experimental data and integration with the SAMMIE computer aided ergonomics design system

Modelling the human body for ergonomic CAD

A recently completed Brite-Euram (European Community) research project was concerned with life-cycle aspects of car seating with Loughborough University being responsible for driver comfort assessment. This was achieved by road and laboratory trials, with the results to be incorporated within the SAMMIE computer-aided ergonomic design system. Driver comfort is in part determined by seat pressure distributions which lead to deformation of the human flesh and the seat and result in uncertainty in the position of important design locations such as the driver's eyepoint. Accommodation of these effects requires a realistic representation of the human body using surface rather than solid representations. Hence a shadow scanning technique was used to capture human body shape which was processed into the DUCT surface modelling system and via IGES files into SAMMIE. Finite element techniques were then used to predict deformations at the seat/driver interface. Having established an anthropometrically correct representation of body shape, current research is aimed at improving the kinematic and analytic capabilities of the human model by introducing a multi-segment spine that can respond to external and internal loadings. This spine model is intended for use in the evaluation of human working postures (such as car driving) where, although the loadings might be viewed as well within human capabilities, previous studies have· shown that back pain or damage might result. The model described is based on an arch representation rather than the pin-jointed rigid link systems which are perhaps more usual, but which have been shown to be deficient in several respects

Biomechanical model of the human spine as an arch

Biomechanical model of the human spine as an arc

Spine modelling and "safe to use" equipment design

Computer human modelling has for sometime been developed and used but even the most sophisticated commercially available human modelling packages do not have an effective spine model. Although some packages have a geometric representation of the spine, they have no analytic or design application functionality. On the other hand back pain and back injuries are well-known to be a major problem and lead to substantial costs to manufacturing industry through enforced absenteeism. The main objective is to provide an answer to the need for a design tool which can consider the range of postures and predict the loads that will be imposed on the spine

Mathematical modelling of human spine and design

Many individuals suffer from back trouble and a large number of sufferers provide a hidden cost to industry, from the increasingly high level of absenteeism. Back pain and injury may result from inadequately designed artefacts and workplaces. In order to achieve better designs which prevent such injuries one has to have a greater understanding of the source of the problems. The mechanics of human spine can be studied by conducting experiments directly on humans in a laboratory. Alternatively mathematical models which represent subtleties and geometric complexities may be studied. Such models of human spine could look at how the spine behaves in specific situations. This paper is about generating a general purpose spine model that is suited a wide range of design applications. The geometric model and the mathematical modelling aspects will be explained. The result of the research infeasibility of range of models representing the spine will also be discussed. The paper will conclude with suggestions on the potential use of human spine models in design

Stability of the spine modelled as an arch

The erector muscles are frequently strained through improper lifting. Stability of the spine is maintained by the muscles, ligaments and pressures inside the body cavities. Modelling of this stability has been achieved using a new arch spine model developed using optimisation techniques. The position of the thrust line in the arch spine model can be used to analyse stability of the spine, and muscle forces introduced to change the position of this thrust line. The erector muscles move the thrust line forward to the centre line of the spine in a weight lifting task in a stooped posture. A method to calculate muscle forces stabilising the spine and to calculate internal forces in the vertebrae is presented. Calculations show that L3/L4 disc loads increase with muscle and ligament forces in the lumbar region

Internal forces in the spine modelled as an arch

The work reported here presents a parametric solid model of the spine, loading systems of the spine and a extracted arch spine model in which the body weight and external loads are treated as forces applied at appropriate points on the spine and muscle and ligament forces are treated as reaction forces applied to both ends of the spine. The model extends the arch spine approach by using optimisation techniques to find a better fitting thrust line compared with the previous arch model in the literature, and calculates the internal forces between the vertebrae in the spine. Case studies show the reasonable values of the internal forces (1.1-1.5 kN) in the arch spine. The values are much less than that of lever models (up to 6.6 kN)

Heterogeneity in the Effect of Common Shocks on Healthcare Expenditure Growth

Health care expenditure growth is affected by important unobserved common shocks such as technological innovation, changes in sociological factors, shifts in preferences and the epidemiology of diseases. While common factors impact in principle all countries, their effect is likely to differ across countries. To allow for unobserved heterogeneity in the effects of common shocks, we estimate a panel data model of health care expenditure growth in 34 OECD countries over the years 1980 to 2012 where the usual fixed or random effects are replaced by a multifactor error structure. We address model uncertainty with Bayesian Model Averaging, to identify a small set of important expenditure drivers from 43 potential candidates. We establish 16 significant drivers of healthcare expenditure growth, including growth in GDP per capita and in insurance premiums, changes in financing arrangements and some institutional characteristics, expenditures on pharmaceuticals, population aging, costs of health administration, and inpatient care. Our approach allows us to derive estimates that are less subject to bias than in previous analyses, and provide robust evidence to policy makers on the drivers that were most strongly associated with the growth in health care expenditures over the past 32 years

Asset prices, exchange rates and the current account

This paper analyses the role of asset prices in comparison to other factors, in particular exchange rates, as a driver of the US trade balance. It employs a Bayesian structural VAR model that requires imposing only a minimum of economically meaningful sign restrictions. We find that equity market shocks and housing price shocks have been major determinants of the US current account in the past, accounting for up to 30% of the movements of the US trade balance at a horizon of 20 quarters. By contrast, shocks to the real exchange rate have been less relevant, explaining about 9% and exerting a more temporary effect on the US trade balance. Our findings suggest that large exchange rate movements may not necessarily be the key element of an adjustment of today's large current account imbalances, and that in particular relative global asset price changes could be a potent source of adjustment