This paper studies the role of sparse regularisation in a properly chosen basis for variational d... more This paper studies the role of sparse regularisation in a properly chosen basis for variational data assimilation (VDA) problems. Specifically, it focuses on data assimilation of noisy and down-sampled observations while the state variable of interest exhibits sparsity in the real or transform domains. We show that in the presence of sparsity, the ‘1-norm regularisation produces more accurate and stable solutions than the classic VDA methods. We recast the VDA problem under the ‘1-norm regularisation into a constrained quadratic programming problem and propose an efficient gradient-based approach, suitable for large-dimensional systems. The proof of concept is examined via assimilation experiments in the wavelet and spectral domain using the linear advectiondiffusion equation.
This paper presents a framework and detailed vision for using immersive virtual reality (VR) envi... more This paper presents a framework and detailed vision for using immersive virtual reality (VR) environments to improve the
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
~ Rm 211 Abstract: Great ecological benefit will be gained if effective barriers can be construct... more ~ Rm 211 Abstract: Great ecological benefit will be gained if effective barriers can be constructed to control the movement of invasive common carp, with feeding techniques that lead to an over-enrichment of nutrients in lakes that dramatically reduces water quality. Bajer et al. (2010) demonstrated that in Minnesota lakes, juvenile carp are recruited from nursery lakes to larger water bodies through small connecting channels. Traditional physical bar- riers are unattractive at these sites as rapid water level changes can damage barriers or the barriers may obstruct flow and promote flooding. The use of bubble curtain barriers, which generate acoustic and hydrodynamic fields to cause an avoidance response in carp, is a class of barrier technology that shows promise for this application. The initial stage of the barrier design was to quantify and measure the physical fields generated by a bubble curtain. An understanding of the physical fields helps to design full barrier systems by exploiting certain features of the bubble curtains. The experimental data revealed that a coarse-bubble curtain created a weaker flow field, but stronger acous- tic field than a fine-bubble diffuser. The subsequent stage of research included barrier tests with live carp using a PIT tag tracking system, which allowed quantification of carp passage over a barrier sans video recording. Three incrementally stronger bubble barriers were designed. A single diffuser design exhibited a mild retarding effect of carp passage time but not on actual passage attempts. Two separate multi-diffuser barriers (varying in configuration and air-supply) both exhibited a sizable decrease in carp passages, ap- proximately 75% in both upstream and downstream directions. The effectiveness of each barrier was determined by comparison with matching control tests without air supplied to the barrier. Carp mobility remained constant between tests, indicating that the two larger
This paper reviews our recent research aimed at gaining a better understanding of the problem of ... more This paper reviews our recent research aimed at gaining a better understanding of the problem of unsteady cavitating flows on lifting surfaces. We have explored this issue with extensive numerical and experimental investigations. This includes the development of new numerical models of cavitating flows including the effects of dissolved incondensable gas and ventilation. Experimental data are drawn from experiments carried out at two different scales in two different water tunnels; one in the US at the Saint Anthony Falls Laboratory (SAFL) and the other at the Versuchsanstalt für Wasserbau (VFW) in Obernach, Germany. Although several foil shapes have been examined, examples are drawn from our NACA 0015 hydrofoil experiments for the sake of brevity.
This paper studies the role of sparse regularisation in a properly chosen basis for variational d... more This paper studies the role of sparse regularisation in a properly chosen basis for variational data assimilation (VDA) problems. Specifically, it focuses on data assimilation of noisy and down-sampled observations while the state variable of interest exhibits sparsity in the real or transform domains. We show that in the presence of sparsity, the ‘1-norm regularisation produces more accurate and stable solutions than the classic VDA methods. We recast the VDA problem under the ‘1-norm regularisation into a constrained quadratic programming problem and propose an efficient gradient-based approach, suitable for large-dimensional systems. The proof of concept is examined via assimilation experiments in the wavelet and spectral domain using the linear advectiondiffusion equation.
This paper presents a framework and detailed vision for using immersive virtual reality (VR) envi... more This paper presents a framework and detailed vision for using immersive virtual reality (VR) environments to improve the
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
~ Rm 211 Abstract: Great ecological benefit will be gained if effective barriers can be construct... more ~ Rm 211 Abstract: Great ecological benefit will be gained if effective barriers can be constructed to control the movement of invasive common carp, with feeding techniques that lead to an over-enrichment of nutrients in lakes that dramatically reduces water quality. Bajer et al. (2010) demonstrated that in Minnesota lakes, juvenile carp are recruited from nursery lakes to larger water bodies through small connecting channels. Traditional physical bar- riers are unattractive at these sites as rapid water level changes can damage barriers or the barriers may obstruct flow and promote flooding. The use of bubble curtain barriers, which generate acoustic and hydrodynamic fields to cause an avoidance response in carp, is a class of barrier technology that shows promise for this application. The initial stage of the barrier design was to quantify and measure the physical fields generated by a bubble curtain. An understanding of the physical fields helps to design full barrier systems by exploiting certain features of the bubble curtains. The experimental data revealed that a coarse-bubble curtain created a weaker flow field, but stronger acous- tic field than a fine-bubble diffuser. The subsequent stage of research included barrier tests with live carp using a PIT tag tracking system, which allowed quantification of carp passage over a barrier sans video recording. Three incrementally stronger bubble barriers were designed. A single diffuser design exhibited a mild retarding effect of carp passage time but not on actual passage attempts. Two separate multi-diffuser barriers (varying in configuration and air-supply) both exhibited a sizable decrease in carp passages, ap- proximately 75% in both upstream and downstream directions. The effectiveness of each barrier was determined by comparison with matching control tests without air supplied to the barrier. Carp mobility remained constant between tests, indicating that the two larger
This paper reviews our recent research aimed at gaining a better understanding of the problem of ... more This paper reviews our recent research aimed at gaining a better understanding of the problem of unsteady cavitating flows on lifting surfaces. We have explored this issue with extensive numerical and experimental investigations. This includes the development of new numerical models of cavitating flows including the effects of dissolved incondensable gas and ventilation. Experimental data are drawn from experiments carried out at two different scales in two different water tunnels; one in the US at the Saint Anthony Falls Laboratory (SAFL) and the other at the Versuchsanstalt für Wasserbau (VFW) in Obernach, Germany. Although several foil shapes have been examined, examples are drawn from our NACA 0015 hydrofoil experiments for the sake of brevity.
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