Stability of liquid bridges between twisted elliptical disks

The influence in the stability of long liquid bridges supported between two elliptical-shaped disks of their main axis relative orientation is investigated. A numerical continuation method capable of finding equilibrium shapes, both stable and unstable, is used to calculate a series of equilibrium shapes supported by disks of increasing eccentricity for different relative orientation of the disks axis. The stable or unstable character of each of the shapes is calculated to determine the position of the stability limit and its characte

Stability of liquid bridges subject to an eccentric rotation

A cylindrical liquid bridge supported between two circular-shaped disks in isorotation is considered. The effect of an offset between the rotation axis and the axis of the two supporting disks (eccentricity) on the stability of the static liquid bridge is investigated. A numerical method is used to find stable and unstable shapes and to determine the stability limit for different values of eccentricity. The calculated stability limits are compared with analytical results, recovering the same behavior. Numerical results have been also compared with the results of an experiment aboard TEXUS-23, recovering the stability limit and the equilibrium shapes

Stability of liquid bridges between an elliptical and a circular supporting disk

A numerical method has been developed to determine the stability limits for liquid bridges held between noncircular supporting disks and the application to a configuration with a circular and an elliptical disk subjected to axial acceleration has been made. The numerical method led to results very different from the available analytical solution which has been revisited and a better approximation has been obtained. It has been found that just retaining one more term in the asymptotic analysis the solution reproduces the real behavior of the configuration and the numerical results

Changes in the thermal properties of polymeric materials induced by molecular orientation: Experimental methods, current understanding and strategies for the application to numerical methods

Trabajo presentado en: Computational Materials Science and Engineering (CoMSE), Atenas, 18 de mayo de 2018The thermo-physical properties of polymers such as thermal conductivity and heat capacity influence the optimization of fabrication processes and the performance of polymeric materials during use. Remarkably, these properties are strongly affected by molecular orientation induced by deformation [1-3]. This talk introduces two complementary experimental methods to characterize the anisotropy in thermal conductivity and its relationship to stress and deformation in polymers subjected to uniaxial extension. Surprisingly, we find: 1) universality of a linear relationship between anisotropy in thermal conductivity and stress known as the stress-thermal rule and 2) that, in contrast to the analogous stress-optic rule, the validity of the stress-thermal rule extends beyond finite extensibility. A growing trend in the design and tuning of polymer manufacturing processes is the use of numerical simulations for the complex non-homogeneous and non-isothermal flows involved. However, while there has been a significant amount of work to include more complete rheological constitutive models into these simulations, the characterization and implementation of material thermo-physical properties and their connection to the micro-structural orientation remains a challenge that has motivated the development of a molecular-to-continuum methodology for the simulation of industrially relevant flows in polymer manufacturing. A portion of this methodology combines the thermal conductivity/stress response with two recent constitutive equations for linear (Rolie Poly) and branched (eXtended Pom-Pom) polymers to obtain predictions for the anisotropy in thermal conductivity. A few examples of interesting and relevant flows and the thermal transport predictions will be givenMolecular to Continuum Investigation of Anisotropic Thermal Transport in Polymers “MCIATTP” Project # 750985Horizon 2020, “MCIATTP” Project # 75098

Results and Experiences from the SODI-IVIDIL Experiment on the ISS

This paper will present a brief summary of the principles of the IVIDIL experiment, as well as the characteristics of the SODI payload and its interfaces with the ground equipment. Also, the work done by E-USOC in terms of preparation of procedures, displays, and setting up of the ground environment will be exposed. To conclude with outcomes of the mission, as well as lessons learned and conclusions

Equilibrium Shapes of Non-axisymmetric Liquid Bridges of Arbitrary Volume in Gravitational Fields and their Potential Energy

Bifurcation diagrams of nonaxisymmetric liquid bridges subject to a lateral gravitational force and to both lateral and axial gravitational forces are found by solving the Young–Laplace equation for the interface by a finite difference method. The potential energy of the equilibrium shapes is also calculated. The results obtained show that the slenderness of the bridge determines whether the breaking of the liquid bridge subject to a lateral gravitational force leads to equal or unequal drops. The stability limits calculated are compared with the ones obtained using asymptotic techniques around the cylinder, the agreement being extremely good for a wide range of the parameters

Comment on “Thickness and Camber Effects in Slender Wing Theory

IN the paper by Plotkin,1 first-order corrections to slender wing theory2 were developed due to spanwise thickness and camber distributions. The velocity potential (x, y, z) calculated in the paper1 actually corresponds to the flow having zero normal velocity at the body contour and a vertical velocity at infinity proportional to the angle of attack [z(x, y, \z\ -> oo) = Ua

Forced Oscillations of Isothermal Liquid Bridges

The forced oscillations of a liquid column held by surface tension forces between two solid supports in a zero gravity environment are analysed by using a linear threedimensional model in which viscosity effects are not considered. Forced oscillations are imposed to the liquid column by vibrating the supporting disks (with particular attention to the in phase or in counter-phase cases), and the response of the liquid bridge (interface deformation and pressure and velocity fields) is obtained. The results arc compared with those obtained with one-dimensional models

Estabilidad de puentes líquidos no axilsimétricos

Se ha desarrollado un método numérico mediante el cual se pueden calcular formas de equilibrio y la estabilidad de puentes líquidos sometidos a muy diversas perturbaciones tanto axilsimétricas como no axilsimétricas. En primer lugar se han linealizado las ecuaciones que describen el comportamiento del sistema fluido en torno a una solución cualquiera conocida. Posteriormente se ha discretizado el problema utilizando un método de diferencias finitas. El sistema de ecuaciones lineales obtenido se ha resuelto empleando un método de continuación que permite encontrar los puntos límite y los puntos de bifurcación que presentan las familias de soluciones que se obtienen al variar un parámetro físico del problema. Más aún, el método permite calcular las ramas de soluciones que se bifurcan de la principal al llegar a un punto de bifurcación, y también permite avanzar por la continuación de la rama principal tras un punto límite. De esta forma se pueden encontrar los diagramas de bifurcación completos que se obtienen al variar un cierto parámetro de la configuración a partir de una solución conocida. Se ha realizado un análisis de los errores que se cometen con el método descrito para justificar la elección del tamaño de la malla utilizada en la discretización del sistema continuo. Gracias a que con el método empleado se pueden calcular soluciones axilsimétricas, se han comparado éstas con las soluciones obtenidas mediante métodos muy contrastados en la literatura. Se han estudiado las formas de equilibrio que se obtienen al aplicar a la configuración una de las siguientes perturbaciones no axilsimétricas: una gravedad no paralela a los ejes de los discos o una excentricidad de los discos soporte. En el estudio combinado de ambos efectos sólo se ha considerado el caso en que la gravedad que actúa sobre el puente líquido está contenida en el plano definido por los ejes de los discos y en dirección perpendicular a los mismos. Para finalizar, se han calculado las energías de las formas de equilibrio obtenidas en cada uno de los casos estudiados. A partir de las energías calculadas se pueden sacar ciertas conclusiones respecto a la estabilidad de las formas de equilibrio y, por tanto, se han podido trazar mapas de estabilidad en el espacio de los parámetros. ABSTRACT A numeric method with which equilibrium shapes and the stability of liquid bridges subjected to a wide variety of axisymmetric or non-axisimmetric perturbations can be calculated, has been developed here. The equations governing the steady shape of the liquid bridge and its boundary conditions have been linearized using a perturbation approach based on a known solution. A finite-difference method has been developed in order to obtain a discrete problem. The discrete linearized problem has been solved using a continuation method which allows to continue through limit and bifurcation points along the main branch and to switch to the bifurcated branch. The complete family of solutions generated varying one of the parameters present in the problem can be found after a known solution. The errors committed by the implemented algorithm have been analyzed to justify the size of the grid that was chosen to obtain the results. The method used allows to obtain stable and unstable axisymmetric shapes, which have been compared with the solutions obtained with other axisymmetric methods that have been widely used in literature. The non-axisymmetric perturbations studied are: a gravity non-parallel to the disk's axes and an eccentricity of the disks. The combined study of both perturbations has been restricted to the case in which the acting gravity is contained in the plane defined by the axes of the disks and is perpendicular to them

A Combination of the eXtended Pom-Pom Model and the Stress-Thermal Rule to Predict Anisotropy in Thermal Conductivity in Non-Linear Polymeric Flows

Trabajo presentado en: 33rd International Conference of the Polymer Processing Society, Cancún, 10 a 14 de diciembre de 2017Advances in polymer processing enables more affordable technologies and significantly impacts the global plastics market which is expected to reach 654 billion USD by 2020. The cost/energy required to manufacture, recycle and dispose polymers is strongly affected by the thermo-physical properties and their dependence on state variables such as temperature and stress. The viscoelastic behavior of polymeric flows under isothermal conditions has been extensively researched. However, most of the processing of polymeric materials occurs under non-isothermal conditions and their implementation in simulations remains a challenge. In particular, flow-induced anisotropy in the thermal conductivity of polymers has been previously omitted in the study of industrially relevant flows. Our work combines evidence of a universal relationship between thermal conductivity and stress tensors (i.e. the stress-thermal rule) with differential constitutive equations for the viscoelastic behavior of polymers to provide predictions for the anisotropy in thermal conductivity in uniaxial, planar, equibiaxial and shear flow in commercial polymers. Special focus is placed on the eXtended Pom-Pom model which captures the non-linear behavior in both shear and elongation flows. The predictions provided by this approach are easily implemented in finite elements packages since the viscoelastic and thermal behavior is described by a single equation. Our results include predictions for the flow-induced anisotropy in thermal conductivity for low density polyethylene as well as validation of the method by comparison with available measurements. Remarkably, this approach allows universal predictions of anisotropy in thermal conductivity to be used in simulations of complex flows in which only the most fundamental rheological behavior of the material has been previously characterized (i.e. no adjusting parameters are needed in addition to those in the constitutive modelHorizon 2020, “MCIATTP” Project # 75098