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

Papers by Dorel Homentcovschi

Research paper thumbnail of Corrections to "an analytical solution for the coupled stripline-like microstrip line problem

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

Research paper thumbnail of Influence of viscosity on the scattering of an air pressure wave by a rigid body: a regular boundary integral formulation

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

Research paper thumbnail of 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.

Research paper thumbnail of 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

Research paper thumbnail of A Computational Study of Non-isothermal Spreading of Liquid Drops

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

ABSTRACT

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

Research paper thumbnail of 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

Research paper thumbnail of On an integral equation

Glasgow Mathematical Journal, Sep 1, 1974

Research paper thumbnail of 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.

Research paper thumbnail of Non-Equilibrium Flow of an Inviscid Gas past a Thin Profile

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.

Research paper thumbnail of 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.

Research paper thumbnail of Numerical analysis of the inviscid incompressible flow in two-dimensional radial-flow pump impellers

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.

Research paper thumbnail of Electrostatic field of a system of aligned electrodes

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.

Research paper thumbnail of 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. >

Research paper thumbnail of A cylindrical multiconductor stripline-like microstrip transmission line

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

An analytical expression for the Maxwell capacitance matrix of a class of cylindrical inhomogeneo... more An analytical expression for the Maxwell capacitance matrix of a class of cylindrical inhomogeneous, multiconductor transmission lines is provided. This class includes cylindrical structures symmetrical with respect to the circuit circle and having a symmetry axis. The effective dielectric constant of the line is found to be the arithmetical mean of the dielectric constants of the two media. Hence, this structure enjoys the main advances of the planar stripline-like microstrip systems. It is also pointed out how to obtain elliptical stripline-like microstrip transmission lines. >

Research paper thumbnail of An intermediate crack model for flaws in piezoelectric solids

Acta Mechanica, Mar 1, 2002

... Page 6. 90 C. Dascalu and D. Homentcovschi Using the relation (18) we obtain the classical ex... more ... Page 6. 90 C. Dascalu and D. Homentcovschi Using the relation (18) we obtain the classical expressions for the stress intensity factors ... (31) Z 7f j 8 -- X 1 -a A numerical procedure based on Gauss-type quadrature formulae, as given by Dragos [18], is employed to solve (31). Let ...

Research paper thumbnail of Stability Considerations Associated with the Meniscoid Particle Band at Advancing Interfaces in Hele-Shaw Suspension Flows

Physical Review Letters, Sep 4, 2000

Research paper thumbnail of Some formulae for numerical differentiation and integration of analytic functions

DOAJ (DOAJ: Directory of Open Access Journals), Feb 1, 1981

Research paper thumbnail of A New Form of the Fundamental Solution of Oseen Equations

Journal of Applied Mathematics and Mechanics, 1980

Research paper thumbnail of Some developments of the CVBEM-application to the mixed boundary value problem for the Laplace equation

Engineering Analysis With Boundary Elements, Mar 1, 1987

The main developments of the CVBEM given in the paper consists in removing the need for approxima... more The main developments of the CVBEM given in the paper consists in removing the need for approximating the boundary curve by a poligonal line and the introduction of the singular boundary elements for the case of re-entrant corners or collision points on the boundary. The paper gives also explicit formulae for solving the mixed Dirichlet-Neumann boundary value problem for two-dimensional Laplace equation by CVBEM. The Fortran program MIXED coded by this idea is applied to some test problems.

Research paper thumbnail of Corrections to "an analytical solution for the coupled stripline-like microstrip line problem

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

Research paper thumbnail of Influence of viscosity on the scattering of an air pressure wave by a rigid body: a regular boundary integral formulation

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

Research paper thumbnail of 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.

Research paper thumbnail of 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

Research paper thumbnail of A Computational Study of Non-isothermal Spreading of Liquid Drops

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

ABSTRACT

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

Research paper thumbnail of 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

Research paper thumbnail of On an integral equation

Glasgow Mathematical Journal, Sep 1, 1974

Research paper thumbnail of 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.

Research paper thumbnail of Non-Equilibrium Flow of an Inviscid Gas past a Thin Profile

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.

Research paper thumbnail of 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.

Research paper thumbnail of Numerical analysis of the inviscid incompressible flow in two-dimensional radial-flow pump impellers

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.

Research paper thumbnail of Electrostatic field of a system of aligned electrodes

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.

Research paper thumbnail of 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. >

Research paper thumbnail of A cylindrical multiconductor stripline-like microstrip transmission line

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

An analytical expression for the Maxwell capacitance matrix of a class of cylindrical inhomogeneo... more An analytical expression for the Maxwell capacitance matrix of a class of cylindrical inhomogeneous, multiconductor transmission lines is provided. This class includes cylindrical structures symmetrical with respect to the circuit circle and having a symmetry axis. The effective dielectric constant of the line is found to be the arithmetical mean of the dielectric constants of the two media. Hence, this structure enjoys the main advances of the planar stripline-like microstrip systems. It is also pointed out how to obtain elliptical stripline-like microstrip transmission lines. >

Research paper thumbnail of An intermediate crack model for flaws in piezoelectric solids

Acta Mechanica, Mar 1, 2002

... Page 6. 90 C. Dascalu and D. Homentcovschi Using the relation (18) we obtain the classical ex... more ... Page 6. 90 C. Dascalu and D. Homentcovschi Using the relation (18) we obtain the classical expressions for the stress intensity factors ... (31) Z 7f j 8 -- X 1 -a A numerical procedure based on Gauss-type quadrature formulae, as given by Dragos [18], is employed to solve (31). Let ...

Research paper thumbnail of Stability Considerations Associated with the Meniscoid Particle Band at Advancing Interfaces in Hele-Shaw Suspension Flows

Physical Review Letters, Sep 4, 2000

Research paper thumbnail of Some formulae for numerical differentiation and integration of analytic functions

DOAJ (DOAJ: Directory of Open Access Journals), Feb 1, 1981

Research paper thumbnail of A New Form of the Fundamental Solution of Oseen Equations

Journal of Applied Mathematics and Mechanics, 1980

Research paper thumbnail of Some developments of the CVBEM-application to the mixed boundary value problem for the Laplace equation

Engineering Analysis With Boundary Elements, Mar 1, 1987

The main developments of the CVBEM given in the paper consists in removing the need for approxima... more The main developments of the CVBEM given in the paper consists in removing the need for approximating the boundary curve by a poligonal line and the introduction of the singular boundary elements for the case of re-entrant corners or collision points on the boundary. The paper gives also explicit formulae for solving the mixed Dirichlet-Neumann boundary value problem for two-dimensional Laplace equation by CVBEM. The Fortran program MIXED coded by this idea is applied to some test problems.