Ana Laverón-Simavilla

Equilibrium shapes of nonaxisymmetric 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.

Effect of a lateral gravitational field on the nonaxisymmetric equilibrium shapes of liquid bridges held between eccentric disks and of volumes equal to those of cylinders

Bifurcation diagrams of nonaxisymmetric cylindrical volume liquid bridges held between nonconcentric circular disks subject to a lateral gravitational force are found by solving the Young-Laplace equation for the interface by a finite difference method. In the absence of lateral gravity, the primary family of liquid bridges that starts with the cylinder when the eccentricity of the disks, e, is zero first loses stability at a subcritical bifurcation point as e increases. Further loss of stability is experienced by the already unstable primary family as a turning point is encountered at yet higher values of the eccentricity. However, the introduction of lateral gravity gl changes entirely the structure of the solutions in that instability always occurs at a turning point with respect to e no matter how small the magnitude of gl. The stability limits calculated are compared with the ones obtained using asymptotic techniques by taking as base solution the cylinder of slenderness Λ=π.

An experimental study of the breakage of liquid bridges at stability limit of minimum volume

An experimental apparatus to study the breaking process of axisymmetric liquid bridges has been developed, and the breaking sequences of a large number of liquid bridge configurations at minimum-volume stability limit have been analyzed. Experimental results show that very close to the breaking moment the neck radius of the liquid bridge varies as t1/3, where t is the time to breakage, irrespective of the value of the distance between the solid disks that support the liquid column.

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.

Fuzzy attitude control for a nanosatellite in low Earth orbit

We design a PID and an adaptive fuzzy controller for the same satellite mission.This is the first time the performances and cost of operation of a PID and an adaptive fuzzy controllers are compared.The fuzzy controller is more efficient than the PID for single manoeuvres with similar accuracy. In order to develop and introduce intelligent systems in the space field, an adaptive fuzzy logic controller is designed for a nanosatellite. Attitude determination and control subsystem (ADCS) and its performance and efficiency are compared with a traditional proportional integrative derivative (PID) controller. Fuzzy controllers have already been studied for satellite attitude control; however their performance has not been compared with the classical PID controllers typically being implemented on board spacecrafts currently. Both controllers have been designed and implemented in order to be tested on board a nanosatellite (QBITO) in a nearby mission (QB50), a constellation of 50 nanosatellites. Due to the requirements imposed by the mission, the orbit, and the significant limitations in the power available in these small spacecrafts, an efficient ADCS is required in order to fulfill the mission objectives. The comparison between the classical PID and the fuzzy controllers shows that the fuzzy controller is much more efficient in single maneuver (up to 65% less power required), achieving better precision in general than the PID. This shows that the use of this type of intelligent control systems is a great advantage over conventional control systems currently being used in satellite attitude control, and open new possibilities of application of intelligent controllers in the field of space technologies.

Cross-waves excited by distributed forcing in the gravity-capillary regime

Cross-wave descriptions based on a boundary forced nonlinear Schrodinger equation, which have been widely used since Jones [J. Fluid Mech. 138, 53–74 (1984)], rely on the assumption that modulations occur on a slow lengthscale compared with the extent of the forcing. This assumption does not hold for recent higher frequency (large aspect ratio) experiments. We extend the established theory of modulated cross-waves in horizontally vibrated containers by including surface tension and, most importantly, a spatially extended forcing term. The resulting amplitude equations provide predictions for onset values, spatial profiles, and temporal modulations that are compared with previous theory and with experimental measurements. The appearance of temporally modulated solutions, confirmed experimentally, is interpreted as the result of weak symmetry-breaking related to the interaction of waves generated at opposite ends.

Instabilities of vibroequilibria in rectangular containers

Vibroequilibria theory, based on minimizing an averaged energy functional, predicts the quasi-equilibrium shape that a fluid volume will take when subjected to high-frequency vibrations. Here we present a detailed comparison of the predictions of vibroequilibria theory with the results of direct numerical simulations in horizontally vibrated rectangular containers, finding very good agreement over a range of parameters. The calculations also reveal an important difference in the behavior between small and large fluid volumes. With dimensionless volume larger than about 0.36, the symmetric vibroequilibria solution suffers a saddle-node instability prior to contact with the container bottom. This saddle-node bifurcation is analyzed using a simplified family of surfaces and shown to persist when gravity is included. Finally, an investigation of dynamic effects is presented, where a strong correlation is found between modulated subharmonic surface waves and the first odd sloshing mode. At large enough amplitu...

GeoFlow - Outcomes from E-USOC's First Mission On-Board Columbus

-USOC is the Spanish User Support and Operations Centre, one of the ten similar centres distributed at different locations in Europe. These centres perform the operations of experiments on board the Columbus Module, the main contribution from the European Space Agency (ESA) to the International Space Station (ISS). The first mission for E-USOC on the Columbus laboratory consisted of executing the GeoFlow experiment, inside the Fluid Science Laboratory (FSL). This experiment studied the movement and behaviour of a fluid contained in between two concentric spheres, representing the geophysical fluid inside the Earth. This fluid motion was observed by means of Interferometry images. The GeoFlow Experiment Container was launched on Space Shuttle Atlantis with the Columbus Module and was installed inside the FSL by a member of the ISS crew. Once placed in the facility, E-USOC operators used telescience to operate the experiment from their control room: Telecommands were sent to control the different GeoFlow subsystems, and telemetry and scientific images from the experiment were received. Achieving successful results from the experiment was a challenging mission, starting in March 2008 and continuing until January 2009, when a malfunction in the GeoFlow Experiment Container forced its return to ground and the interruption of the experiment. The paper will present a general description of the project, address the preparation and execution of such a complex mission and provide an overview of the activities and responsibilities of E-USOC. Furthermore, it will present the outcomes and lessons learned from this project.

Thebas experiment during the spanish soyuz mission cervantes

The educational experiment THEBAS, performed during the Cervantes Mission, was focused on illustrating the principles of dynamics ranging from the classic mechanics of solid bodies to the continuous media mechanics. The objective was to prepare a video for educational purposes. In this article the experimental setup used to perform the experiment is described. It consisted of transparent closed containers (having the same size and total mass) filled with solid spheres of different radii that were periodically oscillated in one dimension. The article also describes the experiment procedures and the technical problems encountered which caused that the experiment did not to work as expected.

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]