Dennis A . Siginer
Presently serves as Distinguished Research Professor at the Universidad de Santiago de Chile in Santiago, Chile.
Previously served as Provost & Senior Deputy Vice Chancellor and Distinguished University Professor at the Botswana International University of Science and Technology in Botswana, which he was pivotal in building from the ground up, and concurrently to his position in Botswana served as Distinguished Research Professor at the Universidad de Santiago de Chile in Santiago, Chile. Prior to that he was Distinguished University Professor of Mechanical Engineering and Mathematics at the Petroleum Institute in Abu Dhabi (now Khalifa University), United Arab Emirates, where he also served as Acting President, Vice President and Dean of the College of Arts and Sciences, which he established as the Founding Dean. Earlier he served as Dean of the College of Engineering at Wichita State University in Wichita, Kansas, USA, Chair of the Mechanical Engineering Department at the New Jersey Institute of Technology in Newark, New Jersey and Professor of Mechanical Engineering at Auburn University in Alabama, USA, and held several visiting positions in France, Japan, Korea, Chile, Brazil, Malaysia, Czech Academy of Sciences, the Russian Academy of Sciences, and NASA. Dr. Siginer holds a PhD from the University of Minnesota, Twin Cities granted in 1982 and a DSc awarded by the Technical University of Istanbul in 1971.
Supervisors: Daniel D. Joseph, Regents Professor Emeritus at the University of Minnesota, Twin Cities, Minneapolis, Minnesota, USA (deceased) for PhD in 1982 and Kazim Cecen, Professor Emeritus at the Technical University of Istanbul, Istanbul, Turkey (deceased) for DSc in 1971
Address: Departamento de Ingeniería Mecánica
Universidad de Santiago de Chile
Avenida Libertador Bernardo O'Higgins No. 3363
Estación Central
Santiago, Chile
Previously served as Provost & Senior Deputy Vice Chancellor and Distinguished University Professor at the Botswana International University of Science and Technology in Botswana, which he was pivotal in building from the ground up, and concurrently to his position in Botswana served as Distinguished Research Professor at the Universidad de Santiago de Chile in Santiago, Chile. Prior to that he was Distinguished University Professor of Mechanical Engineering and Mathematics at the Petroleum Institute in Abu Dhabi (now Khalifa University), United Arab Emirates, where he also served as Acting President, Vice President and Dean of the College of Arts and Sciences, which he established as the Founding Dean. Earlier he served as Dean of the College of Engineering at Wichita State University in Wichita, Kansas, USA, Chair of the Mechanical Engineering Department at the New Jersey Institute of Technology in Newark, New Jersey and Professor of Mechanical Engineering at Auburn University in Alabama, USA, and held several visiting positions in France, Japan, Korea, Chile, Brazil, Malaysia, Czech Academy of Sciences, the Russian Academy of Sciences, and NASA. Dr. Siginer holds a PhD from the University of Minnesota, Twin Cities granted in 1982 and a DSc awarded by the Technical University of Istanbul in 1971.
Supervisors: Daniel D. Joseph, Regents Professor Emeritus at the University of Minnesota, Twin Cities, Minneapolis, Minnesota, USA (deceased) for PhD in 1982 and Kazim Cecen, Professor Emeritus at the Technical University of Istanbul, Istanbul, Turkey (deceased) for DSc in 1971
Address: Departamento de Ingeniería Mecánica
Universidad de Santiago de Chile
Avenida Libertador Bernardo O'Higgins No. 3363
Estación Central
Santiago, Chile
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Papers by Dennis A . Siginer
the third boundary condition with general coefficient is studied using Fourier analysis.
With a general anti-polynomial coefficient a variable number of additional boundary
conditions need to be imposed to determine the eigenvalue uniquely. An additional
boundary condition is required to obtain a unique eigenvalue when the coefficient includes
an essential singularity rather than a pole. In either case explicit solutions are derived.
the third boundary condition with general coefficient is studied using Fourier analysis.
With a general anti-polynomial coefficient a variable number of additional boundary
conditions need to be imposed to determine the eigenvalue uniquely. An additional
boundary condition is required to obtain a unique eigenvalue when the coefficient includes
an essential singularity rather than a pole. In either case explicit solutions are derived.
Energy Considerations in the Flow Enhancement of Viscoelastic Liquids, Journal of Applied Mechanics 60(2):344-352 , 1993.
DOI: 10.1115/1.2900799
The reader is referred to the Journal paper quoted above for full details of the research.
ABSTRACT: Flow enhancement effects due to different waveforms in the tube flow of rheologically complex fluids driven by a pulsating pressure gradient are investigated. It is found that the squarer the waveform the larger the enhancement. In each case the enhancement is strongly dependent on the viscosity function, but the elastic properties also play an important role. We determine that considerable energy savings may be obtained in the transport of viscoelastic liquids if an oscillatory gradient is superposed on a mean gradient. The closer the oscillation to the square wave the larger the energy savings.
velocities, order of magnitude larger increases at certain frequencies of the driving quasi-periodic pressure gradient oscillating about a zero mean is reviewed. Mean secondary flows of non-linear viscoelastic fluids driven by pulsating pressure gradients in straight tubes of non-circular cross section are discussed.
Keywords Non-local stress • Local stress • Linear viscoelasticity • Non-linear viscoelasticity • Smoluchowski diffusion equation • Fokker–Planck diffusion equation • Constant stretch history • Fading memory • Nested integral stress • Order fluids • Consistency with thermodynamics • Rate of dissipation • Burgers equation • Implicit constitutive structures • Canonical forms • Maxwell-like constitutive differential equations • Single integral constitutive equations • Hadamard instability • Dissipative instability
The science of rheology defined as the study of the deformation and flow of matter was virtually single-handedly founded and the name invented by Professor Bingham of Lafayette College in the late 1920s. Rheology is a wide encompassing science which covers the study of the deformation and flow of diverse materials such as polymers, suspensions, asphalt, lubricants, paints, plastics, rubber, and biofluids, all of which display non-Newtonian behavior when subjected to external stimuli and as a result deform and flow in a manner not predictable by Newtonian mechanics.
The development of rheology, which had gotten to a slow start, took a boost during WWII as materials used in various applications, in flame throwers, for instance, were found to be viscoelastic. As Truesdell and Noll famously wrote [Truesdell, C. and Noll, W., the Non-Linear Field Theories of Mechanics, 2nd ed., Springer, Berlin, 1992] “By 1949 all work on the foundations of Rheology done before 1945 had been rendered obsolete.” In the years following WWII, the emergence and rapid growth of the synthetic fiber and polymer processing industries, appearance of liquid detergents, multigrade oils, non-drip paints, and contact adhesives, and developments in pharmaceutical and food industries and biotechnology spurred the development of rheology. All these examples clearly illustrate the relevance of rheological studies to life and industry. The reliance of all these fields on rheological studies is at the very basis of many if not all of the amazing developments and success stories ending up with many of the products used by the public at large in everyday life.
Non-Newtonian fluid mechanics, which is an integral part of rheology, really made big strides only after WWII and has been developing at a rapid rate ever since. The development of reliable constitutive formulations to predict the behavior of flowing substances with non-linear stress–strain relationships is quite a difficult proposition by comparison with Newtonian fluid mechanics with linear stress–strain relationship. The latter does enjoy a head start of two centuries tracing back its inception to Newton and luminaries like Euler and Bernoulli. With the former the non-linear structure does not allow the merging of the constitutive equations for the stress components with the linear momentum equation as it is the case with Newtonian fluids ending up with the Navier–Stokes equations. Thus, the practitioner ends up with six additional scalar equations to be solved in three dimensions for the six independent components of the symmetric stress tensor. The difficulties in solving in tandem this set of non-linear field equations, which may involve both inertial and constitutive non-linearities, cannot be underestimated. Perhaps equally importantly at this point in time in the unfolding development of the science, we are not fortunate enough to have developed a single constitutive formulation for viscoelastic fluids, which may lend itself to most applications and yield reasonably accurate predictions together with the field balance equations. The field is littered with a plethora of equations, some of which may yield reasonable predictions in some flows and utterly unacceptable predictions in others. Thus, we end up with classes of equations for viscoelastic fluids that would apply to classes of flows and fluids, an ad hoc concept at best that hopefully will give way one day to a universal equation, which may apply to all fluids in all motions. In addition the stability of these equations is a very important issue. Any given constitutive equation should be stable in the Hadamard and dissipative sense and should not violate the basic principles of thermodynamics.
Dynamics of tube flow of non-Brownian suspensions and its underpinning field turbulent motion of linear (Newtonian) fluids shows interesting similarities with the flow of viscoelastic fluids in that the secondary flows of viscoelastic fluids in laminar flow driven by unbalanced normal stresses have a counterpart in the turbulent motion of linear fluids in straight tubes of non-circular cross section and in the laminar motion of particle-laden linear fluids. The latter secondary flows are driven by normal stresses due to shear-induced migration of particles. This is a new topic of hot research thrust given its implications in applications. The direction of these normal stresses is opposite of those present in the flow field of a viscoelastic fluid. In fact the tying thread among these seemingly different motions is that all are driven by normal stresses. The turbulent flow of linear fluids is known to have a transversal field due to the anisotropy of the Reynolds stress tensor in non-circular cross sections which entails unbalanced normal Reynolds stresses in the cross section perpendicular to the axial direction. Secondary field also exists in the turbulent flow of linear fluids in circular cross sections if the symmetry is somehow broken due, for example, to unevenly distributed roughness on the boundary, which would again trigger anisotropy of the Reynolds stress tensor. It is not possible to develop a good understanding of the mechanics of the secondary field both in laminar and turbulent motion of particle-laden fluids without a clear grasp of the underlying mechanics of the turbulent secondary field of homogeneous linear fluids. Thus a complete review of both is presented including interesting constitutive similarities with viscoelastic fluids which do arise when certain non-linear closure approximations are made for the anisotropic part of the Reynolds stress tensor.
The impact of the secondary flows on engineering calculations is particularly important as turbulent flows in ducts of non-circular cross section are often encountered in engineering practice. Some examples are flows in heat exchangers, ventilation and air-conditioning systems, nuclear reactors, impellers, blade passages, aircraft intakes, and turbomachinery. If neglected significant errors may be introduced
in the design as secondary flows lead to additional friction losses and can shift the location of the maximum momentum transport from the duct centerline. The secondary velocity depends on cross-sectional coordinates alone and therefore is independent of end effects. It is only of the order of 1–3 % of the streamwise bulk velocity, but by transporting high-momentum fluid toward the corners, it distorts substantially the cross-sectional equal axial velocity lines; specifically it causes a bulging of the velocity contours toward the corners with important consequences
such as considerable friction losses. The need for turbulence models that can reliably predict the secondary flows that may occur in engineering applications is of paramount importance.
Efforts have not been spared to be thorough in the presentation with commentaries about the successes and failures of each theory and the reasons behind them. The link between.....
Palapye, Botswana and Santiago, Chile
Dennis A. Siginer