Thomas Dombrowski

University of North Carolina at Chapel Hill

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Daphne Klotsa

University of North Carolina at Chapel Hill

Amneet Pal Singh Bhalla

San Diego State University

Boyce E. Griffith

University of North Carolina at Chapel Hill

Shannon Jones

University of Cincinnati

Georgios Katsikis

Massachusetts Institute of Technology

Hong T. Nguyen

Arizona State University

Chris H. Rycroft

Lawrence Berkeley National Laboratory

Reagan Howell

University of North Carolina at Chapel Hill

Thomas Dix

University of North Carolina at Chapel Hill

Laura Miller

University of Arizona

Cooperative Institutions

University of North Carolina at Chapel Hill

Applied Physical Sciences (United States)

North Carolina State University

Massachusetts Institute of Technology

Indiana University Bloomington

Harvard University

Lawrence Berkeley National Laboratory

New York University

Courant Institute of Mathematical Sciences

University of Wisconsin–Madison

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Kinematics of a simple reciprocal model swimmer at intermediate Reynolds numbers

Physical Review Fluids (2020)

Thomas Dombrowski Daphne Klotsa

We computationally study the kinematics of a simple model reciprocal swimmer (asymmetric dumbbell) as a function of the Reynolds number (Re) and investigate how the onset and gradual increase of inertia impacts the swimming behavior: a reversal in the swim direction, flow directions, and the swim stroke. We divide the swim stroke into the expansion and compression of the two spheres and relate them to power and recovery strokes. We find that the switch in swim direction also corresponds to a switch in power and recovery strokes. We obtain expressions for the mean swimming velocity by collapsing the net displacement during expansion and compression under power law relationships with respect to Re, the swimmer's amplitude, and the distance between the two spheres. Analyzing the fluid flows, we see the averaged flow field during expansion always resembles a pusher and compression always a puller, but when averaged over the whole cycle, the flow that dominates is the one that occurs during the power stroke. We also relate the power and recovery strokes to the swimming efficiency during times of expansion and compression, and we find that the power stroke is, surprisingly, not always more efficient than the recovery stroke. Our results may have important implications for biology and ultimately the design of artificial swimmers.

Reciprocal

10.1103/physrevfluids.5.063103

Cite

Citations (6)

Pairwise and collective behavior of dumbbell swimmers at intermediate Reynolds numbers

Bulletin of the American Physical Society (2021)

Thomas Dombrowski Hong T. Nguyen Daphne Klotsa

Dumbbell

Source

Cite

Citations (0)

Theories of Origin for the Georgia Kaolins<subtitle>A Review</subtitle>

Clay Minerals Society eBooks (1993)

Thomas Dombrowski

Kaolin is an important industrial mineral in several world markets including uses in paper coating and filling, ceramics, paint, plastics, rubber, ink, fiberglass, cracking catalysts and many other uses (Murray, 1991). The kaolin minerals kaolinite, halloysite, dickite, and nacrite have essentially similar chemical composition but each has important structural and stacking differences. The most common kaolin mineral and the one that is the most important industrially is kaolinite [Al2Si205(OH)4]. Kaolinite can be formed as a residual weathering product, by hydrothermal alteration, and as an authigenic sedimentary mineral. The residual and hydrothermal occurrences are classed as primary and the sedimentary occurrences as secondary. Primary kaolins are those that have formed in situ usually by the alteration of crystalline rocks such as granites and rhyolites. The alteration results from surface weathering, groundwater movement below the surface or action of hydrothermal fluids. Secondary kaolins are sedimentary which were eroded, transported and deposited as beds or lenses associated with other sedimentary rocks. Most kaolin deposits of secondary origin were formed by the deposition of kaolinite which had been formed elsewhere. Some secondary deposits were formed from arkosic sediments that were altered after deposition, primarily by groundwater. There are far more deposits of primary kaolins in the world than secondary kaolin deposits because special geologic conditions are necessary for both the deposition and preservation of secondary kaolins.

Authigenic

10.1346/cms-sp-1.4

Cite

Citations (20)

Experiments and Agent Based Models of Zooplankton Movement within Complex Flow Environments

Biomimetics (2020)

Mustafa Kemal Ozalp Laura Miller Thomas Dombrowski Madeleine Braye Thomas Dix

The movement of plankton is often dictated by local flow patterns, particularly during storms and in environments with strong flows. Reefs, macrophyte beds, and other immersed structures can provide shelter against washout and drastically alter the distributions of plankton as these structures redirect and slow the flows through them. Advection–diffusion and agent-based models are often used to describe the movement of plankton within marine and fresh water environments and across multiple scales. Experimental validation of such models of plankton movement within complex flow environments is challenging because of the difference in both time and spatial scales. Organisms on the scale of 1 mm or less swim by beating their appendages on the order of 1 Hz and are advected meters to kilometers over days, weeks, and months. One approach to study this challenging multiscale problem is to insert actively moving agents within a background flow field. Open source tools to implement this sort of approach are, however, limited. In this paper, we combine experiments and computational fluid dynamics with a newly developed agent-based modeling platform to quantify plankton movement at the scale of tens of centimeters. We use Artemia spp., or brine shrimp, as a model organism given their availability and ease of culturing. The distribution of brine shrimp over time was recorded in a flow tank with simplified physical models of macrophytes. These simplified macrophyte models were 3D-printed arrays of cylinders of varying heights and densities. Artemia nauplii were injected within these arrays, and their distributions over time were recorded with video. The detailed three-dimensional flow fields were quantified using computational fluid dynamics and validated experimentally with particle image velocimetry. To better quantify plankton distributions, we developed an agent-based modeling framework, Planktos, to simulate the movement of plankton immersed within such flow fields. The spatially and temporally varying Artemia distributions were compared across models of varying heights and densities for both the experiments and the agent-based models. The results show that increasing the density of the macrophyte bed drastically increases the average time it takes the plankton to be swept downstream. The height of the macrophyte bed had less of an effect. These effects were easily observed in both experimental studies and in the agent-based simulations.

Brine shrimp

10.3390/biomimetics5010002

Cite

Citations (5)

Reciprocal swimming at intermediate Reynolds number

arXiv (Cornell University) (2022)

Nicholas J. Derr Thomas Dombrowski Chris H. Rycroft Daphne Klotsa

In Stokes flow, Purcell's scallop theorem forbids objects with time-reversible (reciprocal) swimming strokes from moving. In the presence of inertia, this restriction is eased and reciprocally deforming bodies can swim. A number of recent works have investigated dimer models that swim reciprocally at intermediate Reynolds numbers Re ~ 1-1000. These show interesting results (e.g. switches of the swim direction as a function of inertia) but the results vary and seem to be case-specific. Here, we introduce a general model and investigate the behaviour of an asymmetric spherical dimer of oscillating length for small-amplitude motion at intermediate Re. In our analysis we make the important distinction between particle and fluid inertia, both of which need to be considered separately. We asymptotically expand the Navier-Stokes equations in the small amplitude limit to obtain a system of linear PDEs. Using a combination of numerical (Finite Element) and analytical (reciprocal theorem, method of reflections) methods we solve the system to obtain the dimer's swim speed and show that there are two mechanisms that give rise to motion: boundary conditions (an effective slip velocity) and Reynolds stresses. Each mechanism is driven by two classes of sphere-sphere interactions, between one sphere's motion and 1) the oscillating background flow induced by the other's motion, and 2) a geometric asymmetry induced by the other's presence. We can thus unify and explain behaviours observed in other works. Our results show how sensitive, counter-intuitive and rich motility is in the parameter space of finite inertia of particles and fluid.

Reciprocal

10.48550/arxiv.2202.03669

Cite

Citations (1)

Reciprocal swimming at intermediate Reynolds number

Journal of Fluid Mechanics (2022)

N. J. Derr Thomas Dombrowski Chris H. Rycroft Daphne Klotsa

In Stokes flow, Purcell's scallop theorem forbids objects with time-reversible (reciprocal) swimming strokes from moving. In the presence of inertia, this restriction is eased and reciprocally deforming bodies can swim. A number of recent works have investigated dimer models that swim reciprocally at intermediate Reynolds numbers ${\textit Re} \approx 1$ –1000. These show interesting results (e.g. switches of the swim direction as a function of inertia) but the results vary and seem to be case specific. Here, we introduce a general model and investigate the behaviour of an asymmetric spherical dimer of oscillating length for small-amplitude motion at intermediate ${\textit {Re}}$ . In our analysis we make the important distinction between particle and fluid inertia, both of which need to be considered separately. We asymptotically expand the Navier–Stokes equations in the small-amplitude limit to obtain a system of linear partial differential equations. Using a combination of numerical (finite element) and analytical (reciprocal theorem, method of reflections) methods we solve the system to obtain the dimer's swim speed and show that there are two mechanisms that give rise to motion: boundary conditions (an effective slip velocity) and Reynolds stresses. Each mechanism is driven by two classes of sphere–sphere interactions, between one sphere's motion and (1) the oscillating background flow induced by the other's motion, and (2) a geometric asymmetry induced by the other's presence. We can thus unify and explain behaviours observed in other works. Our results show how sensitive, counterintuitive and rich motility is in the parameter space of finite inertia of particles and fluid.

Rossby number

Reciprocal

10.1017/jfm.2022.873

Cite

Citations (9)

Pairwise interactions between model swimmers at intermediate Reynolds numbers

Physical Review Fluids (2022)

Thomas Dombrowski Hong T. Nguyen Daphne Klotsa

How do mesoscale swimmers interact with one another when there is finite inertia? Do they repel, attract, how do they arrange? We numerically study simple model swimmers at intermediate Reynolds numbers and find that they form specific stable pairs depending on system parameters (e.g. Reynolds number). By looking at the flow fields, we relate the assemblies with nonlinear hydrodynamic interactions, namely steady streaming flows and discuss implications for the collective behavior beyond pairs.

10.1103/physrevfluids.7.074401

Cite

Citations (3)

Pairwise and collective behavior between model swimmers at intermediate Reynolds numbers

arXiv (Cornell University) (2021)

Thomas Dombrowski Hong-Quan Nguyen Daphne Klotsa

We computationally studied the pair interactions and collective behavior of asymmetric, dumbbell swimmers over a range of intermediate Reynolds numbers and initial configurations. Depending on the initial positions and the Re, we found that two swimmers either repelled and swum away from one another or assembled one of four stable pairs: in-line and in-tandem, both parallel and anti-parallel. When in these stable pairs, swimmers were coordinated, swum together, and generated fluid flows as one. We compared the stable pairs' speeds, swim direction and fluid flows to those of the single swimmer. The in-line stable pairs behaved much like the single swimmer transitioning from puller-like to pusher-like stroke-averaged flow fields. In contrast, for the in-tandem pairs we discovered differences in the swim direction transition, as well as the stroke-averaged fluid flow directions. Notably, the in-tandem V pair switched its swim direction at a higher $\text{Re}$ than the single swimmer while the in-tandem orbiting pair switched at a lower $\text{Re}$. We also studied a system of 122 swimmers and found the collective behavior transitioned from in-line network-like connections to small, transient in-tandem clusters as the Reynolds number increased, consistent with the in-line to in-tandem pairwise behavior. Details in the collective behavior involved the formation of triples and other many-body hydrodynamic interactions that were not captured by either pair or single swimmer behavior. Our findings demonstrate the richness and complexity of the collective behavior of intermediate-$\text{Re}$ swimmers.

Tandem

Collective Behavior

10.48550/arxiv.2104.10541

Cite

Citations (0)

Swimming in pairs at intermediate Reynolds numbers

APS Division of Fluid Dynamics Meeting Abstracts (2020)

Thomas Dombrowski Daphne Klotsa

Source

Cite

Citations (0)

Transition in motility and collective behavior of a simple, self-propelled swimmer at intermediate Reynolds numbers