TOUVIA MILOH | Tel Aviv University (original) (raw)
Papers by TOUVIA MILOH
Journal of Engineering Mathematics, Mar 10, 2022
Journal of Fluid Mechanics, Feb 10, 2009
We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable di... more We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable dielectric solids following the application of a ‘weak’ transient electric field. To obtain a macro-scale description in the limit of narrow electric double layers (EDLs), we have derived a pair of effective transient boundary conditions directly connecting the electric potentials across the EDL. Within the framework of the above assumptions, these conditions apply to a general transient electro-kinetic problem involving dielectric solids of arbitrary geometry and relative permittivity. Furthermore, the newly derived scheme is applicable to general transient and spatially non-uniform external fields. We examine the details of the physical mechanisms involved in the relaxation of the induced-charging process of the EDL adjacent to polarizable dielectric solids. It is thus established that the time scale characterizing the electrostatic relaxation increases with the dielectric constant of the solid from the Debye time (for the diffusion across the EDL) through the ‘intermediate’ scale (proportional to the product of the respective Debye- and geometric-length scales). Thus, the present rigorous analysis substantiates earlier results largely obtained by heuristic use of equivalent RC-circuit models. Furthermore, for typical values of ionic diffusivity and kinematic viscosity of the electrolyte solution, the latter time scale is comparable to the time scale of viscous relaxation in problems concerning microfluidic applications or micro-particle dynamics. The analysis is illustrated for spherical micro-particles. Explicit results are thus presented for the temporal evolution of electro-osmosis around a dielectric sphere immersed in unbounded electrolyte solution under the action of a suddenly applied uniform field, combining both induced charge and ‘equilibrium’ (fixed charge) contributions to the zeta potential. It is demonstrated that, owing to the time delay of the induced-EDL charging, the ‘equilibrium’ contribution to fluid motion (which is linear in the electric field) initially dominates the (quadratic) ‘induced’ contribution.
Micromachines
A theoretical framework is presented for calculating the polarization, electro-rotation, travelli... more A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based on employing the classical (linearized) Poisson–Nernst–Planck (PNP) formulation under the standard linearized ‘weak-field’ assumption and using the tangent-sphere coordinate system. Explicit expressions are first derived for the axisymmetric AC electric potential governed by the Robin (mixed) boundary condition applied on the dimer surface depending on the resistance–capacitance circuit (RC) forcing frequency. Dimer electro-rotation due to two orthogonal (out-of-phase) uniform AC fields and the corresponding mobility problem of a polarizable dimer exposed to a travelling-wave electric excitation are also analyzed. We pres...
International Journal of Heat and Mass Transfer, 2019
Physical Review Fluids, 2016
The emerging field of plasmofluidics combines plasmonics and nanofluids as an efficient technolog... more The emerging field of plasmofluidics combines plasmonics and nanofluids as an efficient technological platform for manipulating nanoparticles and begetting indirect mixing in aqueous phases due to micro/nano vortices. In a theoretical study, conical metallic structures with small apex angles are considered, and the analytical dispersion relation under optimal operating conditions is derived. It is shown that nanoparticle control can be achieved in way that is similar to optical tweezers.
Micromachines
We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic s... more We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic spherical polarized colloids as well as metallodielectic Janus particles, which are subjected to an arbitrary non-uniform ambient electric field (DC or AC forcing). The analysis is based on employing the linearized ‘standard’ model (Poisson–Nernst–Planck formulation) and on the assumptions of a ‘weak’ field and small Debye scale. In particular, we consider cases of linear and helical time-harmonic travelling-wave excitations and provide explicit expressions for the resulting dielectrophoretic and induced-charge electrophoretic forces and moments, exerted on freely suspended particles. The new analytic expressions thus derived for the linear and angular velocities of the initially uncharged polarizable particle are compared against some available solutions. We also analyze the levitation problem (including stability) of metallic and Janus particles placed in a cylindrical (insulating or co...
Journal of Engineering Mathematics, 2022
of a body falling through calm water. It has been indicated by the authors that even a small dist... more of a body falling through calm water. It has been indicated by the authors that even a small disturbance induced by currents and surface waves may strongly influence the body’s trajectory. Here we present some preliminary results of a similar problem where a symmetric body of revolution is falling in a time-dependent ambient velocity field U r. If the body is small compared to the wavelength of a surface wave, the wave velocity field may be also envisaged as an unsteady non-uniform current. The dynamics of a 3-D slender body falling in a weakly non-uniform unsteady current is investigated. Analytic expressions for the hydrodynamic forces and moments acting on a body moving in a non-uniform current are presented. Numerical simulations of the nonlinear equations of motion of the body are performed. The kinematic parameters of motion and body trajectories are also calculated.
Journal of Fluid Mechanics, 2010
Professor Isaac Goldhirsch, the Raquel and Manuel Klachky Chair of Rheological Flows at the Schoo... more Professor Isaac Goldhirsch, the Raquel and Manuel Klachky Chair of Rheological Flows at the School of Mechanical Engineering of Tel-Aviv University, Israel, died unexpectedly on April 29 at age 60 while on sabbatical leave at the University of Erlangen–Nuremberg, Germany.
Journal of Engineering Mathematics, 1978
Limnology and Oceanography, 1993
Reducing the radiated noise induced by elastic structures in a fluid (water or air) is a practica... more Reducing the radiated noise induced by elastic structures in a fluid (water or air) is a practical problem of immense importance. It is also well known that passive means of decreasing the noise level, especially at low frequencies are generally not very effective. The possibility of using active noise control which are applied directly on the structure has been recently suggested, triggered by the advent of smart structures and the advances in fast micro-processors combined with modern piezoelectric actuators or other induced strain transducers (e.g. Fuller et al 1997). Our interest resides mainly in the technological aspects of fluid-loading of a submerged vibrating structure in the range of frequencies where the compressibility of the fluid medium should be taken into account. Examples for the significance of the interaction between sound and vibration abound in marine engineering (ships, submarine, oil rigs submerged pipes, etc.) as well as in aeronautical, mechanical and nuclea...
A new expression for the Lamd product of prolate spheroidal wave functions is presented in terms ... more A new expression for the Lamd product of prolate spheroidal wave functions is presented in terms of a distribution of multipoles along the axis of the spheroid between its foci (generalizing a corresponding theorem for spheroidal harmonics). Such an “ultimate” singularity system can be effectively used for solving various linear boundary-value problems governed by the Helmholtz equation involving prolate spheroidal bodies near planar or other boundaries. The general methodology is formally demonstrated for the axisymmetric acoustic scattering problem of a rigid (hard) spheroid placed near a hard/soft wall or inside a cylindri cal duct under an axial incidence of a plane acoustic wave.
At the 17-th IWWWFB (2002) Y.Kim, Y. Liu & D. Yue have presented a study of the dynamics of a bod... more At the 17-th IWWWFB (2002) Y.Kim, Y. Liu & D. Yue have presented a study of the dynamics of a body falling through calm water. It has been indicated by the authors that even a small disturbance induced by currents and surface waves may strongly influence the body’s trajectory. Here we present some preliminary results of a similar problem where a symmetric body of revolution is falling in a time-dependent ambient velocity field U r . If the body is small compared to the wavelength of a surface wave, the wave velocity field may be also envisaged as an unsteady non-uniform current. The dynamics of a 3-D slender body falling in a weakly non-uniform unsteady current is investigated. Analytic expressions for the hydrodynamic forces and moments acting on a body moving in a non-uniform current are presented. Numerical simulations of the nonlinear equations of motion of the body are performed. The kinematic parameters of motion and body trajectories are also calculated.
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
We consider the central problem of a non-spherical (ellipsoidal) polarizable (metallic) nanoparti... more We consider the central problem of a non-spherical (ellipsoidal) polarizable (metallic) nanoparticle freely suspended in a conducting liquid phase which is irradiated (heated) by a laser under the Rayleigh (electrostatic) approximation. It is shown that, unlike the case of perfectly symmetric (spherical) particles, the surface temperature of general orthotropic particles exposed to continuous laser irradiation is not uniform! Thus, the induced surface slip (Soret type) velocity may lead to a self-induced thermoosmotic flow (sTOF) about the particle, in a similar manner to the electroosmotic flow driven by the Helmholtz—Smoluchowski slippage. Using the recent advancement in the theory of Lamé functions and ellipsoidal harmonics, we analytically present new solutions for two key physical problems. (i) Heat conduction and temperature distribution inside and outside a conducting laser-irradiated homogeneous tri-axial ellipsoid which is subjected to uniform Joule heating. (ii) Creeping (...
Introduction and Objectives: The problem of sound scattering by vertical structures piercing the ... more Introduction and Objectives: The problem of sound scattering by vertical structures piercing the free surface is of importance for detection and structural integrity assessment. In this study we look at the scattering of an incoming monochromatic sound wave impinging on a vertical flexible (hydroelastic) circular cylinder clamped to the bed floor and piercing the shallow water surface. This model problem is relevant for a variety of engineering applications ranging from off-shore ocean structures to a submarine periscope [1]. The vertical uniform elastic cylinder is taken as hollow (constant thickness) and subject to a distribution of internal pressure (serving as our control) which must be optimized.
Micromachines
By realizing the advantages of using a tri-axial ellipsoidal nano-antenna (NA) surrounded by a so... more By realizing the advantages of using a tri-axial ellipsoidal nano-antenna (NA) surrounded by a solute for enhancing light emission of near-by dye molecules, we analyze the possibility of controlling and manipulating the location of quantum dots (similar to optical tweezers) placed near NA stagnation points, by means of prevalent AC electric forcing techniques. First, we consider the nonlinear electrokinetic problem of a freely suspended, uncharged, polarized ellipsoidal nanoparticle immersed in a symmetric unbounded electrolyte which is subjected to a uniform AC ambient electric field. Under the assumption of small Peclet and Reynolds numbers, thin Debye layer and ‘weak-field', we solve the corresponding electrostatic and hydrodynamic problems. Explicit expressions for the induced velocity, pressure, and vorticity fields in the solute are then found in terms of the Lamé functions by solving the non-homogeneous Stokes equation forced by the Coulombic density term. The particular ...
Mathematical Biosciences, 2016
The European Physical Journal E
An analytic framework is presented for calculating the self-induced thermophoretic velocity of a ... more An analytic framework is presented for calculating the self-induced thermophoretic velocity of a laser-heated Janus metamaterial micro-particle, consisting of two conducting hemispheres of different thermal and electric conductivities. The spherical Janus is embedded in a quiescent fluid of infinite expanse and is exposed to a continuous light irradiation by a defocused laser beam. The analysis is carried under the electrostatic (Rayleigh) approximation (radius small compared to wavelength). The linear scheme for evaluating the temperature field in the three phases is based on employing a Fourier–Legendre approach, which renders rather simple semi-analytic expressions in terms of the relevant physical parameters of the titled symmetry-breaking problem. In addition to an explicit solution for the self-thermophoretic mobility of the heated Janus, we also provide analytic expressions for the slip-induced Joule heating streamlines and vorticity field in the surrounding fluid, for a non-...
Journal of Engineering Mathematics, Mar 10, 2022
Journal of Fluid Mechanics, Feb 10, 2009
We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable di... more We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable dielectric solids following the application of a ‘weak’ transient electric field. To obtain a macro-scale description in the limit of narrow electric double layers (EDLs), we have derived a pair of effective transient boundary conditions directly connecting the electric potentials across the EDL. Within the framework of the above assumptions, these conditions apply to a general transient electro-kinetic problem involving dielectric solids of arbitrary geometry and relative permittivity. Furthermore, the newly derived scheme is applicable to general transient and spatially non-uniform external fields. We examine the details of the physical mechanisms involved in the relaxation of the induced-charging process of the EDL adjacent to polarizable dielectric solids. It is thus established that the time scale characterizing the electrostatic relaxation increases with the dielectric constant of the solid from the Debye time (for the diffusion across the EDL) through the ‘intermediate’ scale (proportional to the product of the respective Debye- and geometric-length scales). Thus, the present rigorous analysis substantiates earlier results largely obtained by heuristic use of equivalent RC-circuit models. Furthermore, for typical values of ionic diffusivity and kinematic viscosity of the electrolyte solution, the latter time scale is comparable to the time scale of viscous relaxation in problems concerning microfluidic applications or micro-particle dynamics. The analysis is illustrated for spherical micro-particles. Explicit results are thus presented for the temporal evolution of electro-osmosis around a dielectric sphere immersed in unbounded electrolyte solution under the action of a suddenly applied uniform field, combining both induced charge and ‘equilibrium’ (fixed charge) contributions to the zeta potential. It is demonstrated that, owing to the time delay of the induced-EDL charging, the ‘equilibrium’ contribution to fluid motion (which is linear in the electric field) initially dominates the (quadratic) ‘induced’ contribution.
Micromachines
A theoretical framework is presented for calculating the polarization, electro-rotation, travelli... more A theoretical framework is presented for calculating the polarization, electro-rotation, travelling-wave dielectrophoresis, electro-hydrodynamics and induced-charge electroosmotic flow fields around a freely suspended conducting dimer (two touching spheres) exposed to non-uniform direct current (DC) or alternating current (AC) electric fields. The analysis is based on employing the classical (linearized) Poisson–Nernst–Planck (PNP) formulation under the standard linearized ‘weak-field’ assumption and using the tangent-sphere coordinate system. Explicit expressions are first derived for the axisymmetric AC electric potential governed by the Robin (mixed) boundary condition applied on the dimer surface depending on the resistance–capacitance circuit (RC) forcing frequency. Dimer electro-rotation due to two orthogonal (out-of-phase) uniform AC fields and the corresponding mobility problem of a polarizable dimer exposed to a travelling-wave electric excitation are also analyzed. We pres...
International Journal of Heat and Mass Transfer, 2019
Physical Review Fluids, 2016
The emerging field of plasmofluidics combines plasmonics and nanofluids as an efficient technolog... more The emerging field of plasmofluidics combines plasmonics and nanofluids as an efficient technological platform for manipulating nanoparticles and begetting indirect mixing in aqueous phases due to micro/nano vortices. In a theoretical study, conical metallic structures with small apex angles are considered, and the analytical dispersion relation under optimal operating conditions is derived. It is shown that nanoparticle control can be achieved in way that is similar to optical tweezers.
Micromachines
We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic s... more We present a theoretical study of the hydrodynamic and electrokinetic response of both metallic spherical polarized colloids as well as metallodielectic Janus particles, which are subjected to an arbitrary non-uniform ambient electric field (DC or AC forcing). The analysis is based on employing the linearized ‘standard’ model (Poisson–Nernst–Planck formulation) and on the assumptions of a ‘weak’ field and small Debye scale. In particular, we consider cases of linear and helical time-harmonic travelling-wave excitations and provide explicit expressions for the resulting dielectrophoretic and induced-charge electrophoretic forces and moments, exerted on freely suspended particles. The new analytic expressions thus derived for the linear and angular velocities of the initially uncharged polarizable particle are compared against some available solutions. We also analyze the levitation problem (including stability) of metallic and Janus particles placed in a cylindrical (insulating or co...
Journal of Engineering Mathematics, 2022
of a body falling through calm water. It has been indicated by the authors that even a small dist... more of a body falling through calm water. It has been indicated by the authors that even a small disturbance induced by currents and surface waves may strongly influence the body’s trajectory. Here we present some preliminary results of a similar problem where a symmetric body of revolution is falling in a time-dependent ambient velocity field U r. If the body is small compared to the wavelength of a surface wave, the wave velocity field may be also envisaged as an unsteady non-uniform current. The dynamics of a 3-D slender body falling in a weakly non-uniform unsteady current is investigated. Analytic expressions for the hydrodynamic forces and moments acting on a body moving in a non-uniform current are presented. Numerical simulations of the nonlinear equations of motion of the body are performed. The kinematic parameters of motion and body trajectories are also calculated.
Journal of Fluid Mechanics, 2010
Professor Isaac Goldhirsch, the Raquel and Manuel Klachky Chair of Rheological Flows at the Schoo... more Professor Isaac Goldhirsch, the Raquel and Manuel Klachky Chair of Rheological Flows at the School of Mechanical Engineering of Tel-Aviv University, Israel, died unexpectedly on April 29 at age 60 while on sabbatical leave at the University of Erlangen–Nuremberg, Germany.
Journal of Engineering Mathematics, 1978
Limnology and Oceanography, 1993
Reducing the radiated noise induced by elastic structures in a fluid (water or air) is a practica... more Reducing the radiated noise induced by elastic structures in a fluid (water or air) is a practical problem of immense importance. It is also well known that passive means of decreasing the noise level, especially at low frequencies are generally not very effective. The possibility of using active noise control which are applied directly on the structure has been recently suggested, triggered by the advent of smart structures and the advances in fast micro-processors combined with modern piezoelectric actuators or other induced strain transducers (e.g. Fuller et al 1997). Our interest resides mainly in the technological aspects of fluid-loading of a submerged vibrating structure in the range of frequencies where the compressibility of the fluid medium should be taken into account. Examples for the significance of the interaction between sound and vibration abound in marine engineering (ships, submarine, oil rigs submerged pipes, etc.) as well as in aeronautical, mechanical and nuclea...
A new expression for the Lamd product of prolate spheroidal wave functions is presented in terms ... more A new expression for the Lamd product of prolate spheroidal wave functions is presented in terms of a distribution of multipoles along the axis of the spheroid between its foci (generalizing a corresponding theorem for spheroidal harmonics). Such an “ultimate” singularity system can be effectively used for solving various linear boundary-value problems governed by the Helmholtz equation involving prolate spheroidal bodies near planar or other boundaries. The general methodology is formally demonstrated for the axisymmetric acoustic scattering problem of a rigid (hard) spheroid placed near a hard/soft wall or inside a cylindri cal duct under an axial incidence of a plane acoustic wave.
At the 17-th IWWWFB (2002) Y.Kim, Y. Liu & D. Yue have presented a study of the dynamics of a bod... more At the 17-th IWWWFB (2002) Y.Kim, Y. Liu & D. Yue have presented a study of the dynamics of a body falling through calm water. It has been indicated by the authors that even a small disturbance induced by currents and surface waves may strongly influence the body’s trajectory. Here we present some preliminary results of a similar problem where a symmetric body of revolution is falling in a time-dependent ambient velocity field U r . If the body is small compared to the wavelength of a surface wave, the wave velocity field may be also envisaged as an unsteady non-uniform current. The dynamics of a 3-D slender body falling in a weakly non-uniform unsteady current is investigated. Analytic expressions for the hydrodynamic forces and moments acting on a body moving in a non-uniform current are presented. Numerical simulations of the nonlinear equations of motion of the body are performed. The kinematic parameters of motion and body trajectories are also calculated.
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
We consider the central problem of a non-spherical (ellipsoidal) polarizable (metallic) nanoparti... more We consider the central problem of a non-spherical (ellipsoidal) polarizable (metallic) nanoparticle freely suspended in a conducting liquid phase which is irradiated (heated) by a laser under the Rayleigh (electrostatic) approximation. It is shown that, unlike the case of perfectly symmetric (spherical) particles, the surface temperature of general orthotropic particles exposed to continuous laser irradiation is not uniform! Thus, the induced surface slip (Soret type) velocity may lead to a self-induced thermoosmotic flow (sTOF) about the particle, in a similar manner to the electroosmotic flow driven by the Helmholtz—Smoluchowski slippage. Using the recent advancement in the theory of Lamé functions and ellipsoidal harmonics, we analytically present new solutions for two key physical problems. (i) Heat conduction and temperature distribution inside and outside a conducting laser-irradiated homogeneous tri-axial ellipsoid which is subjected to uniform Joule heating. (ii) Creeping (...
Introduction and Objectives: The problem of sound scattering by vertical structures piercing the ... more Introduction and Objectives: The problem of sound scattering by vertical structures piercing the free surface is of importance for detection and structural integrity assessment. In this study we look at the scattering of an incoming monochromatic sound wave impinging on a vertical flexible (hydroelastic) circular cylinder clamped to the bed floor and piercing the shallow water surface. This model problem is relevant for a variety of engineering applications ranging from off-shore ocean structures to a submarine periscope [1]. The vertical uniform elastic cylinder is taken as hollow (constant thickness) and subject to a distribution of internal pressure (serving as our control) which must be optimized.
Micromachines
By realizing the advantages of using a tri-axial ellipsoidal nano-antenna (NA) surrounded by a so... more By realizing the advantages of using a tri-axial ellipsoidal nano-antenna (NA) surrounded by a solute for enhancing light emission of near-by dye molecules, we analyze the possibility of controlling and manipulating the location of quantum dots (similar to optical tweezers) placed near NA stagnation points, by means of prevalent AC electric forcing techniques. First, we consider the nonlinear electrokinetic problem of a freely suspended, uncharged, polarized ellipsoidal nanoparticle immersed in a symmetric unbounded electrolyte which is subjected to a uniform AC ambient electric field. Under the assumption of small Peclet and Reynolds numbers, thin Debye layer and ‘weak-field', we solve the corresponding electrostatic and hydrodynamic problems. Explicit expressions for the induced velocity, pressure, and vorticity fields in the solute are then found in terms of the Lamé functions by solving the non-homogeneous Stokes equation forced by the Coulombic density term. The particular ...
Mathematical Biosciences, 2016
The European Physical Journal E
An analytic framework is presented for calculating the self-induced thermophoretic velocity of a ... more An analytic framework is presented for calculating the self-induced thermophoretic velocity of a laser-heated Janus metamaterial micro-particle, consisting of two conducting hemispheres of different thermal and electric conductivities. The spherical Janus is embedded in a quiescent fluid of infinite expanse and is exposed to a continuous light irradiation by a defocused laser beam. The analysis is carried under the electrostatic (Rayleigh) approximation (radius small compared to wavelength). The linear scheme for evaluating the temperature field in the three phases is based on employing a Fourier–Legendre approach, which renders rather simple semi-analytic expressions in terms of the relevant physical parameters of the titled symmetry-breaking problem. In addition to an explicit solution for the self-thermophoretic mobility of the heated Janus, we also provide analytic expressions for the slip-induced Joule heating streamlines and vorticity field in the surrounding fluid, for a non-...