International Journal of Engineering Science, Dec 1, 2014
ABSTRACT This paper is devoted to the experimental investigation of the pipeline flow of low volu... more ABSTRACT This paper is devoted to the experimental investigation of the pipeline flow of low volume fraction suspensions. Our experimental observations of low volume fraction biomass suspensions such as mulch, coffee powder, crushed leaves, in water, show an unusual, non-linear relationship between flow rate and pressure drop which is not observed in homogeneous systems. While it is well known that in Newtonian liquids, the flow rate increases monotonically with the pressure drop, our experiments indicate that increasing pressure drop across the pipe can cause the flow rate to drop at an exponential rate. The observations are seen to be consistent for the varying concentrations and for different kinds of solute particles.
International Journal of Green Energy, Jul 10, 2021
ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested ... more ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number.
Bulletin of the American Physical Society, Mar 4, 2014
strives to communicate the creativity inherent in the sciences to students and the general public... more strives to communicate the creativity inherent in the sciences to students and the general public alike. The project uses connections between the arts and sciences to show the underlying unity and interdependence of the two. The project is planned as one big 'performance' bringing together the two disciplines around the theme of sustainability. In the first phase, physics students learned about and built humanpowered generators including hand cranks and bicycle units. In the second phase, using the generators to power video cameras, art students worked with a visiting artist to make short films on the subject of sustainability, science, and art. The generators and films were showcased at an annual university Physics and Art exhibition which was open to the university and local community. In the final phase, to be conducted, K12 teachers will learn about the project through a professional development workshop and will be encouraged to adapt the experiment for their own classrooms. The last phase will also combine the university and K12 projects for an exhibition to be displayed on Earth Day, 2014.
This paper is devoted to the study and classification of vortex-induced oscillation and the wake ... more This paper is devoted to the study and classification of vortex-induced oscillation and the wake structure of flow past finite cylinders. Experiments were performed in a water tunnel using cylindrical particles hinged in the center of the test section while allowing them one degree of rotational freedom. The speed of flow and aspect ratio of the cylinders were used to vary the Reynolds number in the study between 100 and 5000. The cylinders display different responses to the fluid flow depending upon the Re, ranging from steady orientation, periodic oscillation to autorotation. A hydrogen bubble flow visualization technique was used to examine the vortex structure and supported by image analysis techniques. Specific features of the wake structure such as length of the primary vortex, its frequency and amplitude were analyzed as a function of Re. Our investigations indicate that the frequency of oscillation of the cylinder and the vortex shedding increases monotonically with the Reynolds number. Also, the length of the primary vortex versus Re shows interesting features and reveals possible critical points in the flow when vortex structure changes. In order to better understand qualitative aspects of the cylinder's dynamics that go beyond experiments, a simplistic forced nonlinear pendulum toy model was employed and seen to capture qualitative aspects of the cylinder's dynamics.
ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested ... more ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number.
states, are long known to have their long axis align themselves perpendicular to the direction of... more states, are long known to have their long axis align themselves perpendicular to the direction of flow. This property has been confirmed in sedimentation and horizontal flow setup and the transition to a terminal stable state is believed to coincide with the onset of significant inertial effects in the flow. However, the threshold at which this transition occurs is yet unknown. In this presentation we report a recent experimental study to examine the nature of the transition of prolate spheroids and cylinders of various aspect ratios, from initial to their terminal stable equilibrium. Our experiments reveal that the body reconfigures itself from its initial orientation, continuously to an angle perpendicular to the flow direction, revealing possible steady intermediate angles. Are these "metastable states" real or an artifact of our experiments? Experiments performed on a variety of bodies and using different suspension mechanism show this state to be persistent. A three dimensional numerical simulations performed by us provide strong support for these observations and reveals interesting new findings about the nature of the torque imposed on the body due to the flow at changing Reynolds numbers.
Abstract The principle of least action is a variational principle that states an object will alwa... more Abstract The principle of least action is a variational principle that states an object will always take the path of least action as compared to any other conceivable path. This principle can be used to derive the equations of motion of many systems, and therefore provides a unifying equation that has been applied in many fields of physics and mathematics. Hamilton’s formulation of the principle of least action typically only accounts for conservative forces, but can be reformulated to include non-conservative forces such as friction by using the approach suggested by Wang and co-workers (Lin and Wang, 2014; Wang, 2015). However, it turns out that this modified action is dependent upon the nature and amount of damping in the system and the optimality argument fails to hold for sufficiently large values of the damping coefficient. In this paper, we specifically investigate the modified action principle for the cases of a linearly and cubically damped, nonlinear pendulum.
We study the motion of a rigid sphere falling in a two layer stratified fluid under the action of... more We study the motion of a rigid sphere falling in a two layer stratified fluid under the action of gravity in the potential flow regime. Experiments at moderate Reynolds number of approximately 20 to 450 indicate that a sphere with the precise critical density, higher than the bottom layer density, can display behaviors such as bounce or arrestment after crossing the interface. We experimentally demonstrate that such a critical sphere density decreases as the fluid density transition layer thickness increases, and increases linearly as the bottom fluid density increases with a fixed top fluid density. We propose an estimation of the critical density based on the potential energy, which constitute an upper bound of the critical density with less than 0.05 relative difference within the experimental density regime 0.997 g/cm ∼ 1.09 g/cm.
In this paper we hypothesize that education, especially at the scale of curriculum, should be tre... more In this paper we hypothesize that education, especially at the scale of curriculum, should be treated as a complex system composed of different ideas and concepts which are inherently connected. Therefore, the task of a good teacher lies in elucidating these connections and helping students make their own connections. Such a pedagogy allows students to personalize learning and strive to be ‘creative’ and make meaning out of old ideas. The novel contribution of this work lies in the mathematical approach we undertake to verify our hypothesis. We take the example of a precalculus course curriculum to make our case. We treat textbooks as exemplars of a specific pedagogy and map several texts into networks of isolated (nodes) and interconnected concepts (edges) thereby permitting computations of metrics which have much relevance to the education theorists, teachers and all others involved in the field of education. We contend that network metrics such as average path length, clustering ...
Fluid mechanics is arguably one of the oldest branches of physics, and the literature on this sub... more Fluid mechanics is arguably one of the oldest branches of physics, and the literature on this subject is vast and complex [...]
In this article, we provide a brief review of some generalizations of the second grade fluid mode... more In this article, we provide a brief review of some generalizations of the second grade fluid model. We discuss certain similarities between these fluids and fluids of higher grades, while also describing certain limitations of these models. The new models that we put forth are based upon some interesting experimental results which suggest that not only can normal stress coefficients depend upon the shear rate, but that this dependency is in fact not the same rate as that of shear viscosity variation with shear rate. We then discuss some steady flows of these generalized second grade fluid models.
In this paper, we discuss some well-known experimental observations on self-organization in dissi... more In this paper, we discuss some well-known experimental observations on self-organization in dissipative systems. The examples range from pure fluid flow, pattern selection in fluid–solid systems to chemical-reaction-induced flocking and aggregation in fluid systems. In each case, self-organization can be seen to be a function of a persistent internal gradient. One goal of this article is to hint at a common theory to explain such phenomena, which often takes the form of the extremum of some thermodynamic quantity, for instance the rate of entropy production. Such variational theories are not new; they have been in existence for decades and gained popularity through the Nobel Prize-winning work of theorists such as Lars Onsager and Ilya Prigogine. The arguments have evolved since then to include systems of higher complexity and for nonlinear systems, though a comprehensive theory remains elusive. The overall attempt is to bring out examples from physics, chemistry, engineering, and b...
In this paper we argue that the true aims of education lie in producing ’creative’ individuals wh... more In this paper we argue that the true aims of education lie in producing ’creative’ individuals where creativity is referred to mean motivated, passionate, skilled, adaptable and responsible. Such attitudes to learning, especially in the mathematical and physical sciences, are best produced through a strong undergraduate research program, in fact more so than traditional classroom teaching. Research experience at the undergraduate level instills a deep sense of personalized education and learning that can make the entire university experience extremely pleasurable and of lasting value.
2020 IEEE 20th International Conference on Bioinformatics and Bioengineering (BIBE), 2020
Aggregation of the amyloid-$\beta$(A$\beta$) protein has been implicated in Alzheimer’s disease (... more Aggregation of the amyloid-$\beta$(A$\beta$) protein has been implicated in Alzheimer’s disease (AD). Since, low molecular weight A$\beta$ aggregates are hypothesized to serve as the primary toxic species in AD pathogenesis, significant research has been conducted to understand the mechanistic details of the aggregation process. We previously demonstrated that heterotypic interactions between A$\beta$ and fatty acids (FAs) can lead to competing pathways of A$\beta$ aggregation, termed as the off-pathway; this off-pathway kinetics can also be modulated by FA concentrations as captured by mass action models. We employed ensemble kinetics simulations which uses a system of Ordinary Differential Equations to model the competing on-and off-pathways of $A\beta$ aggregation that were trained and validated by biophysical experiments. However, these models had several rate constants, treated as free parameters to be estimated, which resulted in over-fitting of the model. Hence, in this paper...
We consider, by a combination of asymptotic, computational, and experimental techniques, the flig... more We consider, by a combination of asymptotic, computational, and experimental techniques, the flight time for passive fluid particles flowing past fixed obstacles under the assumptions of potential, stokes, and slightly inertial flow. We observe some intriguing differences between the three cases.
International Journal of Engineering Science, Dec 1, 2014
ABSTRACT This paper is devoted to the experimental investigation of the pipeline flow of low volu... more ABSTRACT This paper is devoted to the experimental investigation of the pipeline flow of low volume fraction suspensions. Our experimental observations of low volume fraction biomass suspensions such as mulch, coffee powder, crushed leaves, in water, show an unusual, non-linear relationship between flow rate and pressure drop which is not observed in homogeneous systems. While it is well known that in Newtonian liquids, the flow rate increases monotonically with the pressure drop, our experiments indicate that increasing pressure drop across the pipe can cause the flow rate to drop at an exponential rate. The observations are seen to be consistent for the varying concentrations and for different kinds of solute particles.
International Journal of Green Energy, Jul 10, 2021
ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested ... more ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number.
Bulletin of the American Physical Society, Mar 4, 2014
strives to communicate the creativity inherent in the sciences to students and the general public... more strives to communicate the creativity inherent in the sciences to students and the general public alike. The project uses connections between the arts and sciences to show the underlying unity and interdependence of the two. The project is planned as one big 'performance' bringing together the two disciplines around the theme of sustainability. In the first phase, physics students learned about and built humanpowered generators including hand cranks and bicycle units. In the second phase, using the generators to power video cameras, art students worked with a visiting artist to make short films on the subject of sustainability, science, and art. The generators and films were showcased at an annual university Physics and Art exhibition which was open to the university and local community. In the final phase, to be conducted, K12 teachers will learn about the project through a professional development workshop and will be encouraged to adapt the experiment for their own classrooms. The last phase will also combine the university and K12 projects for an exhibition to be displayed on Earth Day, 2014.
This paper is devoted to the study and classification of vortex-induced oscillation and the wake ... more This paper is devoted to the study and classification of vortex-induced oscillation and the wake structure of flow past finite cylinders. Experiments were performed in a water tunnel using cylindrical particles hinged in the center of the test section while allowing them one degree of rotational freedom. The speed of flow and aspect ratio of the cylinders were used to vary the Reynolds number in the study between 100 and 5000. The cylinders display different responses to the fluid flow depending upon the Re, ranging from steady orientation, periodic oscillation to autorotation. A hydrogen bubble flow visualization technique was used to examine the vortex structure and supported by image analysis techniques. Specific features of the wake structure such as length of the primary vortex, its frequency and amplitude were analyzed as a function of Re. Our investigations indicate that the frequency of oscillation of the cylinder and the vortex shedding increases monotonically with the Reynolds number. Also, the length of the primary vortex versus Re shows interesting features and reveals possible critical points in the flow when vortex structure changes. In order to better understand qualitative aspects of the cylinder's dynamics that go beyond experiments, a simplistic forced nonlinear pendulum toy model was employed and seen to capture qualitative aspects of the cylinder's dynamics.
ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested ... more ABSTRACT The autorotation and energy harvesting potential of bladeless turbine models are tested in a confined water stream with Reynolds numbers from 20 K to 40 K. Mini bladeless turbine models of various geometrical shapes are 3D-printed using plastic material with low printing density. Experiments were performed using a commercial closed-loop water tank capable of delivering fine incremental speed up to a maximum of 60 cm/s. The cross-cylinder models with low density appear to demonstrate autorotation at high Reynolds numbers. Other turbine models demonstrate either stagnation or oscillation for a wide range of Reynolds numbers. For the cross-cylinder models, the autorotation phenomenon appears to be promoted at lower average flow speed when an upstream asymmetrical obstacle is introduced in the stream. The rotation per minute and energy potential (voltage and current) of the autorotating model are increased with the Reynolds number.
states, are long known to have their long axis align themselves perpendicular to the direction of... more states, are long known to have their long axis align themselves perpendicular to the direction of flow. This property has been confirmed in sedimentation and horizontal flow setup and the transition to a terminal stable state is believed to coincide with the onset of significant inertial effects in the flow. However, the threshold at which this transition occurs is yet unknown. In this presentation we report a recent experimental study to examine the nature of the transition of prolate spheroids and cylinders of various aspect ratios, from initial to their terminal stable equilibrium. Our experiments reveal that the body reconfigures itself from its initial orientation, continuously to an angle perpendicular to the flow direction, revealing possible steady intermediate angles. Are these "metastable states" real or an artifact of our experiments? Experiments performed on a variety of bodies and using different suspension mechanism show this state to be persistent. A three dimensional numerical simulations performed by us provide strong support for these observations and reveals interesting new findings about the nature of the torque imposed on the body due to the flow at changing Reynolds numbers.
Abstract The principle of least action is a variational principle that states an object will alwa... more Abstract The principle of least action is a variational principle that states an object will always take the path of least action as compared to any other conceivable path. This principle can be used to derive the equations of motion of many systems, and therefore provides a unifying equation that has been applied in many fields of physics and mathematics. Hamilton’s formulation of the principle of least action typically only accounts for conservative forces, but can be reformulated to include non-conservative forces such as friction by using the approach suggested by Wang and co-workers (Lin and Wang, 2014; Wang, 2015). However, it turns out that this modified action is dependent upon the nature and amount of damping in the system and the optimality argument fails to hold for sufficiently large values of the damping coefficient. In this paper, we specifically investigate the modified action principle for the cases of a linearly and cubically damped, nonlinear pendulum.
We study the motion of a rigid sphere falling in a two layer stratified fluid under the action of... more We study the motion of a rigid sphere falling in a two layer stratified fluid under the action of gravity in the potential flow regime. Experiments at moderate Reynolds number of approximately 20 to 450 indicate that a sphere with the precise critical density, higher than the bottom layer density, can display behaviors such as bounce or arrestment after crossing the interface. We experimentally demonstrate that such a critical sphere density decreases as the fluid density transition layer thickness increases, and increases linearly as the bottom fluid density increases with a fixed top fluid density. We propose an estimation of the critical density based on the potential energy, which constitute an upper bound of the critical density with less than 0.05 relative difference within the experimental density regime 0.997 g/cm ∼ 1.09 g/cm.
In this paper we hypothesize that education, especially at the scale of curriculum, should be tre... more In this paper we hypothesize that education, especially at the scale of curriculum, should be treated as a complex system composed of different ideas and concepts which are inherently connected. Therefore, the task of a good teacher lies in elucidating these connections and helping students make their own connections. Such a pedagogy allows students to personalize learning and strive to be ‘creative’ and make meaning out of old ideas. The novel contribution of this work lies in the mathematical approach we undertake to verify our hypothesis. We take the example of a precalculus course curriculum to make our case. We treat textbooks as exemplars of a specific pedagogy and map several texts into networks of isolated (nodes) and interconnected concepts (edges) thereby permitting computations of metrics which have much relevance to the education theorists, teachers and all others involved in the field of education. We contend that network metrics such as average path length, clustering ...
Fluid mechanics is arguably one of the oldest branches of physics, and the literature on this sub... more Fluid mechanics is arguably one of the oldest branches of physics, and the literature on this subject is vast and complex [...]
In this article, we provide a brief review of some generalizations of the second grade fluid mode... more In this article, we provide a brief review of some generalizations of the second grade fluid model. We discuss certain similarities between these fluids and fluids of higher grades, while also describing certain limitations of these models. The new models that we put forth are based upon some interesting experimental results which suggest that not only can normal stress coefficients depend upon the shear rate, but that this dependency is in fact not the same rate as that of shear viscosity variation with shear rate. We then discuss some steady flows of these generalized second grade fluid models.
In this paper, we discuss some well-known experimental observations on self-organization in dissi... more In this paper, we discuss some well-known experimental observations on self-organization in dissipative systems. The examples range from pure fluid flow, pattern selection in fluid–solid systems to chemical-reaction-induced flocking and aggregation in fluid systems. In each case, self-organization can be seen to be a function of a persistent internal gradient. One goal of this article is to hint at a common theory to explain such phenomena, which often takes the form of the extremum of some thermodynamic quantity, for instance the rate of entropy production. Such variational theories are not new; they have been in existence for decades and gained popularity through the Nobel Prize-winning work of theorists such as Lars Onsager and Ilya Prigogine. The arguments have evolved since then to include systems of higher complexity and for nonlinear systems, though a comprehensive theory remains elusive. The overall attempt is to bring out examples from physics, chemistry, engineering, and b...
In this paper we argue that the true aims of education lie in producing ’creative’ individuals wh... more In this paper we argue that the true aims of education lie in producing ’creative’ individuals where creativity is referred to mean motivated, passionate, skilled, adaptable and responsible. Such attitudes to learning, especially in the mathematical and physical sciences, are best produced through a strong undergraduate research program, in fact more so than traditional classroom teaching. Research experience at the undergraduate level instills a deep sense of personalized education and learning that can make the entire university experience extremely pleasurable and of lasting value.
2020 IEEE 20th International Conference on Bioinformatics and Bioengineering (BIBE), 2020
Aggregation of the amyloid-$\beta$(A$\beta$) protein has been implicated in Alzheimer’s disease (... more Aggregation of the amyloid-$\beta$(A$\beta$) protein has been implicated in Alzheimer’s disease (AD). Since, low molecular weight A$\beta$ aggregates are hypothesized to serve as the primary toxic species in AD pathogenesis, significant research has been conducted to understand the mechanistic details of the aggregation process. We previously demonstrated that heterotypic interactions between A$\beta$ and fatty acids (FAs) can lead to competing pathways of A$\beta$ aggregation, termed as the off-pathway; this off-pathway kinetics can also be modulated by FA concentrations as captured by mass action models. We employed ensemble kinetics simulations which uses a system of Ordinary Differential Equations to model the competing on-and off-pathways of $A\beta$ aggregation that were trained and validated by biophysical experiments. However, these models had several rate constants, treated as free parameters to be estimated, which resulted in over-fitting of the model. Hence, in this paper...
We consider, by a combination of asymptotic, computational, and experimental techniques, the flig... more We consider, by a combination of asymptotic, computational, and experimental techniques, the flight time for passive fluid particles flowing past fixed obstacles under the assumptions of potential, stokes, and slightly inertial flow. We observe some intriguing differences between the three cases.
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Papers by Ashwin Vaidya