Dorel Homentcovschi - Profile on Academia.edu (original) (raw)

Papers by Dorel Homentcovschi

Fundamental Matrices in Micropolar Fluids

Journal of Applied Mathematics and Mechanics, 1983

Calcul direct des matrices fondamentales bi- et tridimensionnelles et des solutions des equations... more Calcul direct des matrices fondamentales bi- et tridimensionnelles et des solutions des equations des fluides micropolaires incompressibles en mouvement stationnaire

Proceedings of the IEEE, 1982

L=ron2~(4/~)(0.631n(1+no/b)+0.37asinhnu/b] =flon2a (0.802 In (1 + na/b) + 0.471 asinh ru/b]. (12)... more L=ron2~(4/~)(0.631n(1+no/b)+0.37asinhnu/b] =flon2a (0.802 In (1 + na/b) + 0.471 asinh ru/b]. (12) m e error is zero at both extremes and near a/b = 1.1 .) Another Simple formula (relative error <0.01) can be built on the longcoil form (10) 2.78 (The error is zero near u/b = 0.08,0.9, -.) shortcoil form (4) A much doser formula (relative error <0.001) can be built on the 1 2.3 + 1.6 b/u + 0.44 (b/u)2 Here 2.3 = 2.3004 = 1/0.4347 above; 0.44 = 0.4409 = 6/(3n2 -16);

Free Surface Flow About a Cylindrical Obstruction in a Hele Shaw Cell

APS, Nov 1, 1997

ABSTRACT Encapsulation processes are finding increased use in a variety of high technology areas.... more ABSTRACT Encapsulation processes are finding increased use in a variety of high technology areas. For example, in microelectronics packaging, the cylinder-shaped metal bonds also serving as electrical interconnects between a chip and circuit substrate are encapsulated with a particle-laden epoxy material that when cured significantly increases the thermal fatigue life of the interconnects. The encapsulation process involves depositing a metered volume of encapsulant material along some fraction of the chip perimeter and allowing the material to infiltrate by capillary action the narrow gap between chip and substrate. The presence of the cylindrical interconnects makes this gap region multiply-connected and obstructs the flow. A prevalent and debilitating process pathology occurs when the encapsulant material does not completely fill the gap volume and gaseous voids are trapped. The origins of such voids are not well known but we propose a hydrodynamic mechanism for their formation that involves the contact line dynamics on the individual interconnect obstructions. We examine void formation within the context of the Hele Shaw approximation. We present results from both experiments and analysis.

A novel treatment of the sidewall boundary condition in Hele Shaw free surface flow

APS, Nov 1, 1998

ABSTRACT Most studies of free surface flow in Hele Shaw cells either do not consider the problem ... more ABSTRACT Most studies of free surface flow in Hele Shaw cells either do not consider the problem of the contact angle with the side walls or assume that this angle is equal to π/2. As is clear from numerous experiments, the macroscopic advancing contact angle follows a mobility relationship and assumes a continuous range of values. The traditional approach to the problem leads to zero velocity on the contact line when the contact angle is smaller than π/2, and an infinite velocity when the contact angle is larger than π/2. Both cases are physically meaningless. To remove this paradox, we employ a condition similar to the Kutta-Joukowsky condition in aerodynamics. The solution is obtained by conformal mapping of the physical domain onto the exterior of the unit circle in the Z-plane. The kinematic and dynamic boundary conditions on the free surface yield a nonlinear integral equation. This equation is solved by a combined analytic-numeric approach.

Solid-state Electronics, Sep 1, 2020

The basic relationships for a Hall plate with N non-symmetric contacts placed in an arbitrary mag... more The basic relationships for a Hall plate with N non-symmetric contacts placed in an arbitrary magnetic field are a set of N 1 relationships that are necessary and sufficient for the existence of a complex electrostatic potential function. By the application of the boundary conditions, they turn into a linear system of N 1 compatibility conditions involving the terminal voltages and currents. The construction of the basic relationships requires the positions of the contact extremities on the real axis of the canonical domain (the upper half-plane) as well as the electric and magnetic parameters of the Hall device. The conduction and resistance matrices can be obtained easily from the basic relationships. They give an effective method for predicting the performance of both horizontal and vertical Hall effect devices and provide a useful method for designing these types of planar devices. , where V l and V k are the potential values at those two points and is the current flowing through the device from contact i to contact j. The formula was verified for the case when the domain was the upper half-plane > z Re( ) 0 and the contacts were placed along the real axis. Van der Pauw extended the formula to a simple-connected sample by using a conformal mapping and the invariance of the resistances by a conformal mapping. By using the fundamental analogy between thermal and electrical transport, de Boor and Schmidt [15] wrote the thermal equivalent of the van der Pauw equation. Paul, et al. studied a micromachined thermal van der Pauw test structure . Additional studies addressing the interaction of the temperature field with the Hall effect include Joault, et al. [17]

Sensors and Actuators A-physical, Aug 1, 2019

A direct analytical method for determining the Resistance Matrix of a Hall disk with an arbitrary... more A direct analytical method for determining the Resistance Matrix of a Hall disk with an arbitrary number of extended peripheral contacts has been developed. The method does not require the use of any conformal mappings. It works also in the case of large magnetic fields. The resulting explicit formulas involve the angular coordinates of the asymmetrical contacts ends, the sheet resistance, and the Hall angle Â H as inputs. The formulas are obtained through the calculation of some definite integrals of analytical functions with integrable singularities at the end of the peripheral contacts. The method can be used for determining the sheet resistance and the Hall mobility of a circular plate with extended contacts on its boundary by utilizing two measurements similar to those used by van der Pauw's method for pointlike contacts.

IEEE Transactions on Microwave Theory and Techniques, Jun 1, 1989

Proceedings of The Royal Society A: Mathematical, Physical and Engineering Sciences, Apr 22, 2008

This paper gives a regular vector boundary integral equation for solving the problem of viscous s... more This paper gives a regular vector boundary integral equation for solving the problem of viscous scattering of a pressure wave by a rigid body. Firstly, single-layer viscous potentials and a generalized stress tensor are introduced. Correspondingly, generalized viscous double-layer potentials are defined. By representing the scattered field as a combination of a single-layer viscous potential and a generalized viscous double-layer potential, the problem is reduced to the solution of a vectorial Fredholm integral equation of the second kind. Generally, the vector integral equation is singular. However, there is a particular stress tensor, called pseudostress, which yields a regular integral equation. In this case, the Fredholm alternative applies and permits a direct proof of the existence and uniqueness of the solution. The results presented here provide the foundation for a numerical solution procedure.

Linear stability analysis of the flow of a dense suspension with an advancing meniscus in a Hele Shaw cell

APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1999

A theoretical model is discussed for describing the viscous instability associated with the menis... more A theoretical model is discussed for describing the viscous instability associated with the meniscoid band formed by the flow of a dense suspension in a Hele Shaw cell. We model the suspension domain as comprised of two viscous fluids, a lower viscosity fluid representing the displacing suspension and a higher viscosity fluid representing the band suspension. The two fluids are considered miscible and the band volume is allowed to increase with time. The analysis reveals that the instability is generated solely by the increase of volume of the band region.

Viscously driven instability of the meniscoid particle band in Hele Shaw suspension flow

APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1999

We conduct a parametric stability study of the particle band formed at an advancing meniscus in d... more We conduct a parametric stability study of the particle band formed at an advancing meniscus in dense suspension flow in Hele Shaw cells. We use particle image velocimetry to clarify the kinetics of band formation and fingering. We compare our results with the findings of Cardoso and Woods (JFM, 289,pp.351-358 (1995)) who studied the viscous instability of constant volume immiscible

A Computational Study of Non-isothermal Spreading of Liquid Drops

APS Division of Fluid Dynamics Meeting Abstracts, Nov 1, 1996

ABSTRACT

Stability of the Meniscoid Particle Band at Advancing Interfaces in Hele-Shaw Suspension Flows

Erratum to “Uniform asymptotic solutions for lamellar inhomogeneities in plane elasticity” J. Mech. Phys. Solids 48 (2000) 153–173

Journal of The Mechanics and Physics of Solids, Apr 1, 2007

Glasgow Mathematical Journal, Sep 1, 1974

Uniform asymptotic solutions for the two-dimensional potential field problem with joining relations on the surface of a slender body

International Journal of Engineering Science, 1982

Abstract The 2-dimensional potential field in the whole plane with joining relations on the surfa... more Abstract The 2-dimensional potential field in the whole plane with joining relations on the surface of a slender cylindrical body is studied. The inner solution is obtained by means of a regular perturbation problem and the outer solution is represented as a super position of potentials of point sources and point currents distributed on a segment inside the body. The problem is then reduced to a system of integral equations whose solution is obtained by using the method of Handelsman and Keller. As particular cases the Dirichlet and Neumann boundary-value problems for the domain exterior to a slender body are considered. The paper gives the asymptotic expansion of the logarithmic potential on a segment and some quadrature formulae useful for computing the solution as well.

Journal of Applied Mathematics and Mechanics, 1977

This paper wnsiders the steady and linearized motion of a non-equilibrium inviscid gas past a thi... more This paper wnsiders the steady and linearized motion of a non-equilibrium inviscid gas past a thin profile. The form in distributions of the equations of the aerodynamics is used. For the symmetrical profile the problem is completely solved. Elor the case of the profile without thickness the problem calls for a separate consideration of the completely subsonic, intermediate and completely supersonic regimes respectively. I n the first two cases the determination of the function n ( x ) reduces to the resolution of a F r e d h o l m type regular integral equation of the second species. The paper gives the asymptotic solution of the problem for high vuluea of to. For the cme of the completely supersonic reyime the problem is solved to the end. l'he motion of a fluid over a wall is also analysed. Es wird die stationare Stromung eines nicht im Cleichgewicht befindlichen reibungsfreien Gases um ein dunnes Profil auf der Crundlage linearisierter Gleichungen betrachtet. Die in den aerodynamischen Grundgleichungen auftretenden Funktionen werden als Distributionen verstanden. Fur ein symmetrisches Profil wird das Problem vollstandig, gelost. Fur ein dickeloses Profil ist eine getrennte Betrachtuny des Unterschull-, des schallnahen und des Uberschallbereiches notwendig. I n den ersten beiden Fullen fuhrt die Bestimrnuny der P'unktion n ( x ) auf eine reyulare Bredholmsche lnteyrulgleichung zweiter Art; in der Arbeit wird die asymptotische Lbsung des Problems f u r groJe Werte von q, gegeben. Fur den Fall der reinen liberschallstriimung wird das Problem allgemein gelost. Die 8tromung uber eine Wand wird ebenfulls analysiert. B pa6oTe paccMaTpwsaeTcn naneapqr3aposannoe o6TeIcanae nerioToporo Tomoro I I ~O @ H ~H n e m w m ra3oM B nepawosecnoM cocMomtm. klcnonba YH)TCII aepomwamsecme ypaBnenm, nanncanmre B 06061uen~x @ynKqaax. B cnyae cmMMeTpmecKoro npo@mn npo6nema nonnocTbIo penraeTcH. B c n ysae me npo@kmn 6e3 Tonmanbr npo6nevy enenyeT paanemno paccMaTpmaTb, a aMenHo, nnrl 06nac~eii J ~O ~B Y I C O B O ~~, nepexonnoii a c~epx3sy~o~ot%. B nepsax ~B Y X cn yqasx onpeaenenme @yniwrnrn n ( x ) CBOAMTCH K pewenam neIcoToporo peryaHpnoro MwrerpanbHoro ypamenarl Tma Qpenronbma moporo pona. $ J ~H 6on~ruax anasen~ii q, B pa6o~e AaHo acmmToTasecKoe pemenrne npo6nem.r. rIpH nonbIIoM csepx3~yrro~om peHimMe, aanasa pe-UaeTcn no IFonua. Anannampye~c~ TaIwe AsmtcIiae ~c a ~i c o c ~a O I E O ~O cTeIiIcn.

A linearized theory of three-dimensional airfoils in nonuniform flow

Acta Mechanica, Mar 1, 1976

SummaryStarting from the linearized hydrodynamic equations in distributions and using the methods... more SummaryStarting from the linearized hydrodynamic equations in distributions and using the methods developed in [1], [2] and [3], the integro-differential equation which characterizes the motion of an incompressible perfect fluid past an airfoil in a two-dimensional parallel shear flow is deduced.For wings whose width is small with respect to the span an equation analogous to that of Prandtl is deduced.The equations obtained generalize those corresponding to the case of uniform flow.ZusammenfassungVon den linearisierten hydrodynamischen Gleichungen ausgehend wird, unter Verwendung der in [1], [2] und [3] entwickelten Methoden, die Integro-Differentialgleichung der Bewegung einer inkompressiblen idealen Flüssigkeit längs eines Tragflügels in zweidimensionaler paralleler Scherströmung hergeleitet.Für Flügel mit im Vergleich zur Spannweite kleiner Tiefe wird ein Analogon zur Prandtlschen Gleichung gewonnen.Die erhaltenen Gleichungen verallgemeinern die entsprechenden Fälle der gleichförmigen Anströmung.

Engineering Analysis With Boundary Elements, Dec 1, 1998

The ¯ow through a two-dimensional centrifugal impeller ®tted with equiangular blades of arbitrary... more The ¯ow through a two-dimensional centrifugal impeller ®tted with equiangular blades of arbitrary geometry is investigated using a combination of conformal mapping with a boundary element technique. The blades can be thin or thick of arbitrary cross-section. A theoretical analysis and a numerical procedure are developed to determine the pressure distributions along the blade.

Journal of Electrostatics, Aug 1, 1991

This paper provides an analytical expression for the electrostatic field of a system of aligned e... more This paper provides an analytical expression for the electrostatic field of a system of aligned electrodes, the case of the piecewise homogeneous medium (two different dielectrics on the two sides of electrodes ) and that of one or two infinite electrodes are discussed too. The paper provides also the Maxwell capacitance matrix of the system. The problem is of a proper interest and can be also used as a model problem for analysing other steady electromagnetic systems.

An analytical solution to the microstrip line problem

IEEE Transactions on Microwave Theory and Techniques, Jun 1, 1990

An analytical method for determining the line capacitance of a microstrip line is presented. The ... more An analytical method for determining the line capacitance of a microstrip line is presented. The solution is exact, but it is expressed by means of the solution of an infinite system of linear equations whose coefficients are the result of certain numerical quadratures. The analysis is carried out for the case of two dielectric substrates. Changes to include additional stratified layers are readily available using the transfer matrix method described by P.M. van Berg et al. (1985). Comparison of the results obtained using the proposed formula with those obtained using exact formulas (available in particular cases) shows that, in cases of practical interest, it is sufficient to consider only the first two equations in the above-mentioned infinite set of linear equations. >