C.J. Baker’s research while affiliated with University of Birmingham and other places

Lodging is a major constraint to increasing the global productivity of maize (Zea Maize L.). The objectives of this paper are to: i) describe a model for stem and root lodging in maize, ii) calibrate the anchorage strength component of the model, iii) evaluate the model’s applicability by assessing its capacity to explain effects of crop husbandry on lodging risk and iv) investigate the potential to further develop the lodging model to predict lodging risk at an early enough growth stage for tactical agronomic action to minimise lodging risk. The study involved a multidisciplinary collaboration between crop scientists, wind engineers and geospatial scientists in the UK and China. Three field experiments with plant population density and nitrogen (N) fertiliser rate treatments were conducted in the UK and China to develop and test the lodging model. Plant characteristics associated with lodging were measured in the experiments after flowering. An existing model of cereal anchorage strength that uses the spread of the root plate as its primary input was demonstrated to be applicable for maize and calibrated for this crop species. The lodging model’s predictions of the effects of plant population and N fertiliser on lodging risk were consistent with published observations. The lodging model calculated that increasing the plant population significantly reduced the anchorage and stem failure wind speeds in all experiments, thus increasing the risk of lodging. This effect was primarily due to increased plant population reducing the spread of the root plate and the stem strength. Changes in N fertiliser had a smaller effect on the lodging associated plant characters. A sensitivity analysis showed that stem failure wind speed was influenced most by variation in stem strength and root failure wind speed was influenced most by variation in the spread of the root plate. This study has shown that the leaf area index measured at leaf 4, 6 or 8 stages is a good indicator of a crop’s future risk of lodging, which demonstrates the potential to develop the model into a practical tool for predicting lodging risk in time for tactical agronomic decisions to be made during the crop’s growing period.

This paper presents a novel methodology for calculating the risk of a train overturning accident due to tornadoes. It applies a recently developed model of tornado wind fields to the complex case of a moving vehicle passing at different distances from the centre of a moving tornado. The wind speed and direction relative to the vehicle can thus be calculated. Through the use of quasi-steady force coefficients and an allowance for dynamic effects, this allows aerodynamic forces and moment time histories on the vehicle to be calculated. A parametric investigation of the effects of tornado size, strength and translational speed, and vehicle speed is then presented. A stochastic analysis methodology is then set out that allows the probability of a train overturning accident to be determined for specified statistical distributions of tornado parameters and vehicle operational parameters. It is shown that the reduction of train speed at times when tornadoes are expected would lead to a very significant reduction in accident risk. Finally the requirements for further work to refine the methodology are set out – specifically the need for statistical distributions of tornado parameters and for force and moment coefficients obtained from proper physical or numerical simulations of tornado characteristics.

This paper presents a novel conceptual design framework which takes into account the direct wind loads and pressure loads acting on a structure due to the passing of a tornado. Furthermore, for the first time, the potential damage due to debris impact has been incorporated enabling a holistic assessment of structural loading to be considered. The model is built on a recently developed wind and pressure field model that captures the main features of tornadoes, which is used to generate a large number of tornado wind and pressure field realisations from which values of particular load effects can be determined. A cumulative distribution function of load effect is thus derived, which can be combined with tornado climatology probabilities to determine load effects at a particular risk level. This use of this framework is illustrated through two examples – the direct wind and pressure loads on a low-rise portal frame structure, and the debris loads on a medium rise rectangular structure.

Air pollution from diesel emissions is becoming an increased international concern, and whilst attention has been primarily focused on the automotive industry, concerns have also been raised about emissions from diesel rail vehicles. This paper reports an extensive series of measurements made at the Birmingham New Street station, a major rail interchange in the Midlands of England, with a mix of diesel and electric train movements, which is of particular concern because of the enclosed nature of the platforms. The monitoring campaign consisted of diffusion tube measurements to measure nitrogen dioxide at a large number of different locations throughout and around the station. These were followed by detailed measurements of oxides of nitrogen, particulate matter, carbon dioxide and black carbon (a diesel tracer) at a smaller number of sites at the platform level. The results are analysed to give concentrations over a wide variety of time scales, and long- and short-term averages are presented. It is shown that the concentrations of nitrogen dioxide, in particular, significantly exceed the European Union (EU) and Department of Environment, Food and Rural Affairs (DEFRA) limits. The effects of ambient wind conditions and individual train movements are also considered. Recommendations are made for possible remedial measures and for future work to more fully understand the physical mechanisms involved.

This paper describes the derivation of a simple yet realistic engineering model of tornado wind and pressure fields. This novel model is shown to be capable of providing a method for predicting wind speed and pressure time histories and debris impact energies that can ultimately be used in the development of a rational risk-based design methodology for tornado wind loads on buildings. A stationary one-cell tornado vortex is first considered, and the circumferential and vertical velocities and pressure profiles derived from a simple assumption for radial velocity (that is bounded in the radial and vertical directions) and the use of the Euler equations. The generalisation of this model to a two-cell tornado form is then set out. This model is then used to investigate the trajectories of wind borne debris in tornado wind fields, and for the first time, this analysis reveals the important dimensionless parameters of the problem and the parameter boundary between falling and flying debris. An asymptotic long time solution for debris paths is also derived.

This paper explores the results obtained from an innovative physical model study which examined wind induced forces and pressures on a 1:25 scale model of a Class 390 Pendolino at a 30° yaw angle. For the first time, the work considers in detail the differences between moving model experiments and static experiments. Differences between the static and moving experiments are observed in the pressure distribution on the nose region of the train, however over the rest of the train the differences between the two sets of experiments are within the experimental uncertainty. The overall side, lift and rolling moment coefficients acting on the train are also shown to agree. This paper provides the scientific underpinning embedded within the current industrial guidelines and once and for all, demonstrates that in terms of the overall mean aerodynamic side and lift forces and rolling moment coefficients, static experiments are sufficient.

The lodging of cereal crops due to high wind and rain is of considerable significance in many parts of the world, leading to major economic losses and yield reductions. In earlier papers the authors have developed a model of the lodging of winter wheat that identified the major parameters of the problem and enabled the relationship between root and stem lodging to be examined. It has formed the basis of a methodology used in the UK for guidance to farmers and agronomists on ways of reducing lodging risk. However the authors would be the first to acknowledge that there are limitations to the model that make it difficult to apply for a wide range of crops - particularly in the specification of the wind field and the root / soil interaction, and in allowing for stem lodging elsewhere than at the base of the stem. This paper thus describes the development of a generalised model that overcomes these shortcomings. After a discussion of the lodging phenomenon in general and a description of earlier work, the basis of the new model is set out, based upon a mechanical model of the wind / plant /soil interactions that capture most of the important physical processes. The manner in which this model can be applied to clarify the nature of the lodging process and calculate lodging risk through a simple graphical formulation is discussed. In particular simple formulae are defined for lodging risk that are a function of a small number of dimensionless variables with identified physical meanings. The model is then applied to the lodging of wheat, oat and oilseed rape crops and considers the sensitivity of the risk calculations to uncertainties in the model parameters. In general it is suggested that the risk of lodging can be determined from very simple functions of dimensionless stem and root lodging velocities.

Little is known of the behaviour of transient air velocities and dynamic pressure loads generated by high-speed trains in confined spaces, or whether current methodologies for assessing transient gust loads in open spaces can be used in confined spaces. Experiments have been carried out in which a moving-model high-speed train passed walls, a partially-enclosed tunnel, and single-track tunnels with a variety of cross-sectional areas and lengths. An open air control experiment has also been carried out. The train model was a simplified 1/25 scale four-carriage ICE2 train travelling at 32 m/s. Cobra Probes measured the three-dimensional air velocity components at various positions inside the structures. The results show that the peak gust magnitudes increase in all confined cases compared to the open air. In tunnels, a ‘piston effect’ appears to have been a dominant cause of the increases in the peak gust magnitudes, as well as prolonged winds occurring before and after the train passed the probes. The tunnel length impacted considerably on the flow characteristics, and the partially-enclosed tunnel showed further increases in the gusts due to high lateral and vertical velocities.