Roger David Braddock

Free-surface flow in porous media and periodic solution of the shallow-flow approximation

Abstract The equations describing the flow of liquid in a porous medium with a free surface are expanded when the shallow-flow assumption holds. Second-order theory is used to describe the propagation of steady periodic motion in the medium, driven by the oscillating level of a reservoir in contact with it. A linearized solution of the second-order theory is compared with a numerical solution and is found adequate even when the amplitude of the motion is comparable to the mean depth of the liquid. The predictions of the analysis are found in good agreement with two laboratory experiments.

The New Morris Method; an efficient second order screening method

The New Morris Method was proposed by Campolongo and Braddock [Reliab. Engng Syst. Saf. 64 (1999) 1] as an extension of the Morris Method [Technometrics 33 (1991) 161] to include estimation of two-factor interaction effects. An undetected programming error prevented Campolongo and Braddock from appreciating the efficacy of the method. Testing on an analytic function reveals that the method is more powerful and efficient than previously thought.

Effect of fiber orientation on fiber wetting processes

The current work incorporates a microscopic study of the effect of fiber orientation on the fiber wetting process and flow of liquid droplets along filter fibers when subjected to airflow and gravity forces. Glass filter fibers in various combinations were oriented at various angles within a plane defined by the airflow direction and were supplied with distilled water in aerosol form. The behavior and flow of the liquid collected by the fibers were observed and measured using a specially developed microscope cell, detailed in the paper. The experimental results were compared to a theoretical model developed to describe the behavior. The theory and experimental results showed good agreement. The developed theory allows an optimum angle to be determined for the internal filter fiber structure in the design of wet filters. A sensitivity analysis of the model was conducted to determine the most important parameters. This will aid design of wet filtration systems such that maximal self-cleaning can be accomplished with minimal water use.

On the simulation of root water extraction: examination of a minimum energy hypothesis.

An alternative procedure for calculating root water extraction from different depths of a soil profile is proposed. The procedure is based on the concept that the root water extraction entails energy expenditure by the plant and that the plant seeks to minimize the total rate of energy expenditure during water uptake. The model, therefore, considers root water extraction to be a minimization problem whose solution can be sought using a dynamic programming framework. We tested the model by simulating the variations of the soil water content using the time and depth of a maize-sorghum intercrop experiment reported for an 8-day drying cycle by Ozier-Lafontaine et al. (Plant and Soil 204:183-201, 1998). Simulated patterns follow the observed water content distribution quite well. Furthermore, results from numerical experiments show that the model is capable of simulating a range of water extraction patterns in a realistic manner. Patterns of water extraction from uniformly wet soil profiles follow those of the root distribution with depth. The extraction rate is highest in the section where the root length density is also highest. Once the soil profile dries out, water extraction patterns cease to bear any similarity to root distribution. Model simulations also show increased root activity at greater depths when the top sections of the soil dry out. Generally, the model avoids the need to make any prior assumptions about the pattern of the root water extraction.

Coupling between ocean biota and atmospheric aerosols: Dust, dimethylsulphide, or artifact?

[1] Two hypotheses that postulate interactions between ocean biota and aerosols in the atmosphere have generated substantial research into marine systems. The stimulation of phytoplankton photosynthesis by the provision of iron, a micronutrient contained in deposited aeolian dust (the Iron Hypothesis), and the contribution of dimethylsulphide (DMS) produced by marine ecosystems to the atmospheric burden of aerosols (the CLAW Hypothesis) have been the focus of much research. Satellite sensors, such as the Seaviewing Wide Field-of-view Sensor (SeaWiFS) now provide moderate-resolution time series of measurements of the optical properties of the oceans and atmosphere over most of the Earth’s surface. These data provide an unprecedented opportunity to investigate the ubiquity of biotic linkages between the ocean and atmosphere at the global scale. We analyzed 5 years of SeaWiFS 8-day fields of two variables, chlorophyll concentration and aerosol optical depth, for the global oceans. This first global, multiyear approach does not yet allow unequivocal conclusions, as satellite measurements of chlorophyll can be influenced by aerosol properties of the atmosphere and several variables we do not yet examine are likely to play a role. We find correlation between optical properties of the ocean and atmosphere over much of the globe, in particular the midlatitudes. While some regional analyses indicate that SeaWiFS chlorophyll retrievals are biased by dust in the atmosphere, our results do not support the existence of widespread bias in the SeaWiFS products, but are consistent with global-scale couplings posited by the Iron and CLAW hypotheses.

Particle Bounce During Filtration of Particles on Wet and Dry Filters

This paper experimentally examines the bounce and immediate re-entrainment of liquid and solid monodisperse aerosols under a stable filtration regime (precake formation) by wet and dry fibrous filters. PSL and DEHS were the solid and liquid aerosols, respectively, used in four monodisperse sizes of 0.52, 0.83, 1.50, and 3.00 w m. Three different fibrous filters were used to filter the aerosol streams, and the efficiency of the filtration process for each aerosol type under dry and wet regimes was measured. It was found that the solid particles generally exhibited a lower fractional filtration efficiency than liquid particles, although this difference decreased in the smaller size fractions. The difference between solid and liquid efficiencies was found to be greatest in the 1.5 w m size range. As particle sizes of liquid/solid aerosols and filtration parameters were similar, this difference is most likely to be due to the effect of particle bounce and or immediate re-entrainment occurring inside the filter, with the greater efficiency of filtration of the liquid particles being due to their greater capacity to plastically/elastically deform in order to absorb the impact forces. However, for the wet filtration regime (each fibre of the filter was coated by a film of water), no significant difference in filtration efficiency was detectable between solid and liquid aerosols. Therefore, the conclusion can be drawn that the either the bounce effect of the particles is inhibited by the liquid film, or the filtration conditions in the wet filter are so different that the aerosol properties are less significant with respect to capture.

Feed-Forward Artificial Neural Network Model For Forecasting Rainfall Run-Off

This paper presents the results of a blind test of the ability of a feed-forward artificial neural network to provide out-of-sample forecasting of rainfall run-off using real data. The results obtained are comparable with the results obtained using best methods currently available. The focus of the paper has been an easily repeatable experiment applied to rainfall and run-off data for a catchment area; which particular catchment was not revealed to the experimenters, i.e. a blind experiment. To this end, a simple model has been specified, and the architecture of the neural network and the data preparation procedures adopted are discussed in detail. The results are presented and discussed in detail and the extent to which the system was found to be non-linear is quantified.

A MATLAB method of lines template for transport equations

Abstract Many environmental problems involve diffusion and convection processes, which can be described by partial differential equations (PDEs). This paper will describe the development of a MATLAB template that generates a numerical solution to PDEs using the method of lines. The template will be applied to various unsaturated flow problems within soil physics to demonstrate the versatility of the method. In particular, the template will generate solutions for three cases (1) one-dimensional Richards’ equation for vertical infiltration; (2) coupled one-dimensional Richards’ equation and solute transport equation for horizontal water and contaminant flow; and (3) two-dimensional Richard’s equation for unsaturated flow over a complex geometry. Where possible, the results from the template will be compared against analytical solutions to determine the accuracy of the numerical solution. In addition, the paper will provide a discussion on possible extensions to the template and future directions.

Removal of aerosols by bubbling through porous media

Aerosols can be filtered on fibrous filters with or without the pres ence of circulating water. The wet filtration leads to the formation of bubbles within the filter as the carrier gas passes through. This provides alternate mechanisms for the removal of aerosols. Experiments are described to investigate the effects of the irrigating fluid and to compare the efficiency of wet and dry filtration. The results indicate a marked increase in efficiency of filtration of the wet filter as compared with the dry filter.

Modeling dimethylsulphide production in the upper ocean

Dimethylsulphide (DMS) is produced by upper ocean ecosystems and emitted to the atmosphere, where it may have an important role in climate regulation. Several attempts to quantify the role of DMS in climate change have been undertaken in modeling studies. We examine a model of biogenic DMS production and describe its endogenous dynamics and sensitivities. We extend the model to develop a one-dimensional version that more accurately resolves the important processes of the mixed layer in determining the ecosystem dynamics. Comparisons of the results of the one-dimensional model with an empirical relationship that describes the global distribution of DMS, and also with vertical profiles of DMS in the upper ocean measured at the Bermuda Atlantic Time Series, suggest that the model represents the interaction between the biological and physical processes well on local and global scales. Our analysis of the model confirms its veracity and provides insights into the important processes determining DMS concentration in the oceans.