Simulations of Elastic Particles in Viscous Fluid Flows,
and Magnetically Tuned Porous Electrode Formation in
Electrochemical Flow Capacitor
Howard H. Hu
Department of Mechanical Engineering and Applied Mechanics
University of Pennsylvania
时间：10月21日（周二）下午3:30 ~ 5:00
地点：力学一楼239会议室
Abstract:
In this presentation, I will discuss two different topics as the
title has suggested. In the first topic, I will present a
monolithic finite element solver for fluid-structure interactions to
simulate dynamics of elastic objects in viscous fluids. The
particles are assumed to be neutrally buoyant
and composed of neo-Hookean material with constant shear modulus.
I will also introduce a polarization technique to establish a
theory described by a set of coupled nonlinear, first-order ODEs
for the finite-strain, time-dependent response of an ellipsoidal
elastic particle in shear and uniaxial extensional flows under
Stokes flow conditions. In shear flow, we identified three types
of particle motion: tank-treading (TT), trembling (TR) and
tumbling (TU) as the functions of the particle elastic shear
modulus, its initial shape, and the flow shear rate. In an
extensional flow, an initially ellipsoidal (elliptical) elastic
particle simultaneously stretches and rotates, tending to deform
into a stable, ellipsoidal shape with the initial major axis
aligned with the extension direction. However, steady-state
solutions may not exist when the particle stiffness is lower than
a certain critical value. Finally, I will describe a new
application of our monolithic solver to simulate the free
swimming of caenorhabditis-elegans in a viscous fluid.
In the second topic, I will describe an electrochemical flow
capacitor (EFC), where high surface area, conducting,
magnetizable porous particles suspended in an electrolyte
solution flow from one storage tank to another through a
charging/discharging device between collecting electrodes
(collector). In the collector, the particles quickly aggregate
to form percolated, electrically conducting networks that
facilitate electron flow. To achieve a highly conductive and
rapidly assembling network, a high concentration suspension is
needed. To facilitate easy pumping, a low concentration
suspension is desired. To speed up the network formation
process and overcome these conflicting requirements, we use
magnetizable colloids. The particles will acquire a magnetic
moment in the presence of an external magnetic field. The
magnetic moment will reversibly disappear as soon as the
magnetic field is removed. The magnetic field will be applied
during the charge and discharge phases to accelerate the
formation of electrically connected networks when desired and
will be removed when it is time to flow the slurry and refresh
the contents in the collector. I will discuss our study of the
network assembly process, and the estimate for the network
connectivity and electric properties.
About the speaker:
Prof. Hu received his Ph.D. degree in Aerospace Engineering,
University of Minnesota, in 1992. He joined University of
Pennsylvania as an assistant professor in 1992 and became a
professor in 2009. His research focus is on modeling complex
flows involving multiphase and polymeric fluids, particularly
flows with solid particles, liquid drops, and gas bubbles. His
group has been developing numerical techniques for simulating
motions of large numbers of particles in those multiphase
systems. They are engaged in understanding and controlling the
particulate flows in various microfluidic applications through
electrophoresis and dielectrophoresis. He has published
more than 80 papers in journals and proceedings, including J.
Fluid Mech., J. Comput. Phys., Phys. Rev. Lett., etc. He was
elected as the Fellow of American Society of Mechanical
Engineering (2009) and the Fellow of American Physical Society
(2011).
Electrochemical Flow Capacitor
Howard H. Hu
Department of Mechanical Engineering and Applied Mechanics
University of Pennsylvania
时间：10月21日（周二）下午3:30 ~ 5:00
地点：力学一楼239会议室
Abstract:
In this presentation, I will discuss two different topics as the
title has suggested. In the first topic, I will present a
monolithic finite element solver for fluid-structure interactions to
simulate dynamics of elastic objects in viscous fluids. The
particles are assumed to be neutrally buoyant
and composed of neo-Hookean material with constant shear modulus.
I will also introduce a polarization technique to establish a
theory described by a set of coupled nonlinear, first-order ODEs
for the finite-strain, time-dependent response of an ellipsoidal
elastic particle in shear and uniaxial extensional flows under
Stokes flow conditions. In shear flow, we identified three types
of particle motion: tank-treading (TT), trembling (TR) and
tumbling (TU) as the functions of the particle elastic shear
modulus, its initial shape, and the flow shear rate. In an
extensional flow, an initially ellipsoidal (elliptical) elastic
particle simultaneously stretches and rotates, tending to deform
into a stable, ellipsoidal shape with the initial major axis
aligned with the extension direction. However, steady-state
solutions may not exist when the particle stiffness is lower than
a certain critical value. Finally, I will describe a new
application of our monolithic solver to simulate the free
swimming of caenorhabditis-elegans in a viscous fluid.
In the second topic, I will describe an electrochemical flow
capacitor (EFC), where high surface area, conducting,
magnetizable porous particles suspended in an electrolyte
solution flow from one storage tank to another through a
charging/discharging device between collecting electrodes
(collector). In the collector, the particles quickly aggregate
to form percolated, electrically conducting networks that
facilitate electron flow. To achieve a highly conductive and
rapidly assembling network, a high concentration suspension is
needed. To facilitate easy pumping, a low concentration
suspension is desired. To speed up the network formation
process and overcome these conflicting requirements, we use
magnetizable colloids. The particles will acquire a magnetic
moment in the presence of an external magnetic field. The
magnetic moment will reversibly disappear as soon as the
magnetic field is removed. The magnetic field will be applied
during the charge and discharge phases to accelerate the
formation of electrically connected networks when desired and
will be removed when it is time to flow the slurry and refresh
the contents in the collector. I will discuss our study of the
network assembly process, and the estimate for the network
connectivity and electric properties.
About the speaker:
Prof. Hu received his Ph.D. degree in Aerospace Engineering,
University of Minnesota, in 1992. He joined University of
Pennsylvania as an assistant professor in 1992 and became a
professor in 2009. His research focus is on modeling complex
flows involving multiphase and polymeric fluids, particularly
flows with solid particles, liquid drops, and gas bubbles. His
group has been developing numerical techniques for simulating
motions of large numbers of particles in those multiphase
systems. They are engaged in understanding and controlling the
particulate flows in various microfluidic applications through
electrophoresis and dielectrophoresis. He has published
more than 80 papers in journals and proceedings, including J.
Fluid Mech., J. Comput. Phys., Phys. Rev. Lett., etc. He was
elected as the Fellow of American Society of Mechanical
Engineering (2009) and the Fellow of American Physical Society
(2011).