derek jackson | University of Ulster (original) (raw)

Papers by derek jackson

Ocean & Coastal Management, 2010

Journal of Sedimentary Research, 2011

Encyclopedia of Planetary Landforms, 2014

Coastal Engineering 1996, 1997

Sedimentary Geology, Nov 1, 1996

Most models to predict aeolian sand transport rates incorporate a threshold shear velocity term t... more Most models to predict aeolian sand transport rates incorporate a threshold shear velocity term to specify the condition when sand flux begins. This term usually takes the form derived by the equation of Bagnold (1936). When shear velocity falls below the threshold value, the transport equations predict an immediate cessation of sediment movement. However, under some conditions this is not so and transport may continue for a period. This paper describes field observations of an inertia-like process that be considered when wind velocity fluctuates at near-threshold values. This study found that, although wind conditions had decreased to below threshold levels, transport was still taking place. Therefore using standard models that incorporate a threshold term, an underestimation of sediment transport would occur.

Heating of water for domestic use is often the largest single point of energy consumption in mode... more Heating of water for domestic use is often the largest single point of energy consumption in modern homes. By augmenting conventional water heating systems with a solar thermal heat system, the consumption of conventional fuels is reduced. This saves the customer money over time and reduces the use of non-renewable resources. Solar energy is free and renewable. It makes sense

Geomorphology, Apr 1, 2009

Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topograph... more Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18-22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach. Horizontal traps, electronic and integrating, measured sediment flux on the supra-tidal beach. Results show that offshore wind flow deviated from its original direction in the lee of the dune (seaward of foredune). The change in direction was not a simple steering of flow to a singular new direction, but rather flow separation resulting in turbulent multidirectional flow — including reversal. Traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds. Data from sediment traps, wind and observational evidence have been used to argue that sedimentation was occurring in this zone. When budgeting for sediment movement within beach-dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation, particularly in post-storm recovery.

Int J Heat Fluid Flow, 1999

This paper is concerned with the response of fluid temperature within a heated pipe to imposed ex... more This paper is concerned with the response of fluid temperature within a heated pipe to imposed excursions of flow rate. Experiments are reported in which measurements of wall temperature and local fluid temperature were made with fully developed turbulent flow of water in a uniformly heated tube during and after ramp-up excursions of flow rate between steady initial and final values. The fluid temperature measurements were made using a traversable temperature probe incorporating a thermocouple capable of responding to turbulent fluctuations of temperature. Local values of mean temperature and RMS temperature fluctuation were obtained by ensemble averaging the results from many tests in which the same flow excursion was applied in a very repeatable manner with fixed values of inlet fluid temperature and heat flux. Further measurements were made under conditions of steady flow rate at a number of values over the range covered in the transient flow experiments. The results obtained in the experiments with transient flow show that there is a significant delay in the variation of ensemble-averaged wall temperature and striking perturbations in the variations of RMS fluctuation of wall temperature and local fluid temperature. These stem from the delayed response of turbulence to the imposed excursions of flow rate. They provide independent confirmation of ideas concerning the modelling of time scales for the production and diffusion of turbulence in pipe flow which were developed by the present authors in the course of earlier work. Ensemble-averaged local fluid temperature also varies in an unusual manner. Instead of falling monotonically with increase of flow rate, as might be expected, it starts to rise at some stage, reaches a peak value and then falls again. The release of heat stored in the pipe wall contributes to this behaviour. Computational simulations of the present experiments were performed using a spatially fully developed formulation of the equations for unsteady turbulent flow and heat transfer in a boundary layer utilising turbulence models of low Reynolds number, k–ε type. Comparisons between predicted and measured variations of temperature are presented in the paper. These show that the predictions differ significantly from model to model and that detailed agreement with experiment is not obtained using any of the models. However, certain interesting features of the observed temperature variations, such as a delay in the response of outer wall temperature and perturbations in local fluid temperature, are present in the computed results.

Journal of Coastal Research, Feb 1, 2011

ABSTRACT The presence of multiple dune forms inside Martian craters is evident on much of the rec... more ABSTRACT The presence of multiple dune forms inside Martian craters is evident on much of the recent HiRISE imagery available. Typically multiple length scales are present with progressively smaller bedform features superimposed on larger dunes, giving rise to complex but regular topographical patterns. There is a need to understand the airflow behaviour over these features to investigate if the formational pattern and orientation of the bedforms correspond to localised wind flow forcing. Using computational fluid dynamics (OpenFoam) we present preliminary findings within Mars’ Proctor Crater, examining a dune area of 4.5km x 5.0km running with a computational cell resolution of 5m x 5m. A range of wind speed and directions are investigated and results are compared to bedform orientation and length scale. Superimposed over recent HiRISE imagery, results reveal a distinctive relationship between steered airflow and localised bedform orientation, mapping orthogonally onto the crestal ridges and dune troughs present. This work has important implications for the reconstruction of aeolian dunes within craters on Mars and can help lend further support to studies examining recent activity of Martian dune migration.

Geomorphology, Apr 1, 2013

Http Dx Doi Org 10 1080 17445647 2014 956820, Sep 15, 2014

Ocean & Coastal Management, 2010

Journal of Sedimentary Research, 2011

Encyclopedia of Planetary Landforms, 2014

Coastal Engineering 1996, 1997

Sedimentary Geology, Nov 1, 1996

Most models to predict aeolian sand transport rates incorporate a threshold shear velocity term t... more Most models to predict aeolian sand transport rates incorporate a threshold shear velocity term to specify the condition when sand flux begins. This term usually takes the form derived by the equation of Bagnold (1936). When shear velocity falls below the threshold value, the transport equations predict an immediate cessation of sediment movement. However, under some conditions this is not so and transport may continue for a period. This paper describes field observations of an inertia-like process that be considered when wind velocity fluctuates at near-threshold values. This study found that, although wind conditions had decreased to below threshold levels, transport was still taking place. Therefore using standard models that incorporate a threshold term, an underestimation of sediment transport would occur.

Heating of water for domestic use is often the largest single point of energy consumption in mode... more Heating of water for domestic use is often the largest single point of energy consumption in modern homes. By augmenting conventional water heating systems with a solar thermal heat system, the consumption of conventional fuels is reduced. This saves the customer money over time and reduces the use of non-renewable resources. Solar energy is free and renewable. It makes sense

Geomorphology, Apr 1, 2009

Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topograph... more Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18-22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach. Horizontal traps, electronic and integrating, measured sediment flux on the supra-tidal beach. Results show that offshore wind flow deviated from its original direction in the lee of the dune (seaward of foredune). The change in direction was not a simple steering of flow to a singular new direction, but rather flow separation resulting in turbulent multidirectional flow — including reversal. Traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds. Data from sediment traps, wind and observational evidence have been used to argue that sedimentation was occurring in this zone. When budgeting for sediment movement within beach-dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation, particularly in post-storm recovery.

Int J Heat Fluid Flow, 1999

This paper is concerned with the response of fluid temperature within a heated pipe to imposed ex... more This paper is concerned with the response of fluid temperature within a heated pipe to imposed excursions of flow rate. Experiments are reported in which measurements of wall temperature and local fluid temperature were made with fully developed turbulent flow of water in a uniformly heated tube during and after ramp-up excursions of flow rate between steady initial and final values. The fluid temperature measurements were made using a traversable temperature probe incorporating a thermocouple capable of responding to turbulent fluctuations of temperature. Local values of mean temperature and RMS temperature fluctuation were obtained by ensemble averaging the results from many tests in which the same flow excursion was applied in a very repeatable manner with fixed values of inlet fluid temperature and heat flux. Further measurements were made under conditions of steady flow rate at a number of values over the range covered in the transient flow experiments. The results obtained in the experiments with transient flow show that there is a significant delay in the variation of ensemble-averaged wall temperature and striking perturbations in the variations of RMS fluctuation of wall temperature and local fluid temperature. These stem from the delayed response of turbulence to the imposed excursions of flow rate. They provide independent confirmation of ideas concerning the modelling of time scales for the production and diffusion of turbulence in pipe flow which were developed by the present authors in the course of earlier work. Ensemble-averaged local fluid temperature also varies in an unusual manner. Instead of falling monotonically with increase of flow rate, as might be expected, it starts to rise at some stage, reaches a peak value and then falls again. The release of heat stored in the pipe wall contributes to this behaviour. Computational simulations of the present experiments were performed using a spatially fully developed formulation of the equations for unsteady turbulent flow and heat transfer in a boundary layer utilising turbulence models of low Reynolds number, k–ε type. Comparisons between predicted and measured variations of temperature are presented in the paper. These show that the predictions differ significantly from model to model and that detailed agreement with experiment is not obtained using any of the models. However, certain interesting features of the observed temperature variations, such as a delay in the response of outer wall temperature and perturbations in local fluid temperature, are present in the computed results.

Journal of Coastal Research, Feb 1, 2011

ABSTRACT The presence of multiple dune forms inside Martian craters is evident on much of the rec... more ABSTRACT The presence of multiple dune forms inside Martian craters is evident on much of the recent HiRISE imagery available. Typically multiple length scales are present with progressively smaller bedform features superimposed on larger dunes, giving rise to complex but regular topographical patterns. There is a need to understand the airflow behaviour over these features to investigate if the formational pattern and orientation of the bedforms correspond to localised wind flow forcing. Using computational fluid dynamics (OpenFoam) we present preliminary findings within Mars’ Proctor Crater, examining a dune area of 4.5km x 5.0km running with a computational cell resolution of 5m x 5m. A range of wind speed and directions are investigated and results are compared to bedform orientation and length scale. Superimposed over recent HiRISE imagery, results reveal a distinctive relationship between steered airflow and localised bedform orientation, mapping orthogonally onto the crestal ridges and dune troughs present. This work has important implications for the reconstruction of aeolian dunes within craters on Mars and can help lend further support to studies examining recent activity of Martian dune migration.

Geomorphology, Apr 1, 2013

Http Dx Doi Org 10 1080 17445647 2014 956820, Sep 15, 2014