Zero-gravity Environment Research Articles

On the thermocapillary migration of a growing or shrinking drop

Prior thermocapillary migration experiments revealed that the rate of migration of a partially miscible drop, slowly moving within a vertical temperature gradient, obeyed in a quasi-static sense a theoretical prediction for an immiscible drop. The hydrodynamic theory for a partially miscible drop is developed here for circumstances where the thermal effects of mass transfer are negligible. Analysis shows that rates of growth or shrinkage in these experiments were too small to affect the flow. Nevertheless, for finite growth of shrinkage rates the migration velocity is given by a quasi-static interpretation of the immiscible theory. Moreover, similar results are found for a partially miscible gas bubble moving under conditions of finite Reynolds and small Marangoni numbers in a zero-gravity environment.

Response of a rotating finite annular liquid layer to various axial excitations in zero gravity

A solidly rotating finite annular liquid layer consisting of non-viscous liquid is subjected to different axial harmonic excitations in a zero-gravity environment. The response of the free liquid surface elevation and the velocity in the radial, angular and axial directions has been determined in the elliptic forcing frequency range Ω > 2Ω 0 and in the hyperbolic range Ω < 2Ω 0 for different diameter ratios.

Response of a viscous liquid layer to pitching-and roll-excitation in zero-gravity environment

The response of a viscous liquid layer to pitching- and roll excitation has been determined. For a simplified analytical treatment the no-slip condition at the top and the bottom of the liquid column has been abandoned in the pitching case. The response of the free liquid surface displacement and the velocity distribution has been determined as a function of the reduced frequency ωa2/ν for various surface tension parameters σa/ρv2. Due to viscosity the resonance amplitudes are finite and disappear for higher modes and shorter liquid layers. The velocity distribution, effective moment of inertia and effective damping was obtained for the liquid layer in roll excitation.

Steady-State and Irregular Motions of a System with Friction Under Harmonic Excitation∗

Abstract A system with one degree of freedom in the form of a parallelogram linkage with friction-affected constraints is considered. Position-, velocity-, and acceleration-dependent kinetic friction is studied as a source of nonlinear effects. Steady-state and irregular motions of the system under different kinds of harmonic excitation (by force, moment, and motion) and the influence of gravity and zero-gravity environments are investigated.

Response of an annular cylindrical liquid column to various axial excitations in zero-gravity

An annular liquid layer is subjected in a zero-gravity environment to different harmonic axial excitations. The liquid is treated as frictionless and is held together by free surface tension, which acts as the restoring force. The response of the system has been determined for the free surface elevation and the velocity distribution. It was found, that the first resonance response is sharply tuned and could easily be missed in a sweeping experiment. Damping was introduced in the resonance terms.

Lunar Astronomical Observatories: Design Studies

The best location in the inner solar system for the grand observatories of the 21st century may be the moon. A multidisciplinary team including university students and faculty in engineering, astronomy, physics, and geology, and engineers from industry is investigating the moon as a site for astronomical observatories and is doing conceptual and preliminary designs for these future observatories. Studies encompass lunar facilities for radio astronomy and astronomy at optical, ultraviolet, and infrared wavelengths of the electromagnetic spectrum. Although there are significant engineering challenges in design and construction on the moon, the rewards for astronomy can be great, such as detection and study of earth-like planets orbiting nearby stars, and the task for engineers promises to stimulate advances in analysis and design, materials and structures, automation and robotics, foundations, and controls. Fabricating structures in the reduced-gravity environment of the moon will be easier than in the zero-gravity environment of earth orbit, as Apollo and space-shuttle missions have revealed. Construction of observatories on the moon can be adapted from techniques developed on the earth, with the advantage that the moon's weaker gravitational pull makes it possible to build larger devices than are practical on earth.

Response of a viscous liquid column to various pitch-excitations

The response of a viscous liquid column to counter-directional one-sided and phase-different pitching excitation of the walls between which the column is placed has been presented in zero-gravity environment. For a simplified analytical treatment the no-slip condition has been abandoned. Velocity distribution and free surface displacement have been determined as functions of the “reduced” forcing frequency Ωα 2 v . Since the upper and lower wall of the liquid column are changing locally their distance, the liquid column always moves into the converging wall space.

THERMOCAPILLARY MIGRATION OF SLIGHTLY DEFORMED DROPLETS

ABSTRACT A small viscous droplet which is suspended in an immiscible liquid in a zero-gravity environment can be made to migrate by subjecting the system to an external temperature gradient. This so-called thermocapillary migration occurs since the surface tension of the interface is a function of temperature. If inertial effects are negligible and the interface is clean, the shape of the migrating droplet remains spherical. However, when inertial effects are significant or when surfactants are present at the interface, the droplet assumes a prolate or oblate spheroidal shape. In this work we calculate the change in the net migration velocity of the droplet which results from such a deformation. This is done by solving the requisite viscous flow problem in the deformed geometry by perturbation, in conjunction with a generalization of the so-called Lorentz reciprocal theorem which simplifies the calculations. It is found that the migration velocity could increase, decrease or remain unchanged depending on ...

Response of a liquid column to one-sided axial excitation in zero gravity

A finite cylindrical liquid column consisting of incompressible and frictionless liquid is subjected at the upper end to axial harmonic excitation. The liquid system is in a zero-gravity environment and is held together by surface tension, which acts as restoringforce. The response of the system has been determined for the free surface elevation and the velocity distribution. In addition the transient behavior was investigated. Damping has been introduced in the resonance terms. It was found, that the first resonance response is sharply tuned and could easily be missed by a sweeping experiment. The investigation was performed for the preparation of the German-D-2 Spacelab-Mission “LICORE”.

Response of a rotating finite annular liquid layer to axial excitation

A solidly rotating finite annular liquid layer consisting of nonviscous liquid is subjected to axial harmonic excitation in a zerogravity environment. The response of the free liquid surface elevation and the velocity in radial and axial direction have been determined in the elliptic forcing frequency range Ω>2Ω0 and in the hyperbolic range Ω>2Ω0 for different diameter ratios.

Non-linear oscillations of a non-viscous cylindrical liquid system in weightlessness condition

For an immiscible cylindrical liquid system in a circular cylindrical container and a liquid layer around a rigid center core consisting of incompressible and non-viscous liquid the natural non-linear frequencies are determined, if the system is in a zero-gravity environment. The frequencies are determined as a function of the surface elevation and are presented as backbone curves.

Response of an annual cylindrical liquid column in zero-gravity

An annular liquid layer is subjected in a zero-gravity environment to harmonic axial- and pitching excitation. The liquid is treated as frictionless and is held together by free surface tension, which acts as the restoring force. The response of the system has been determined for the free surface elevation and the velocity distribution. It was found, that the first resonance response is sharply tuned and could easily be missed in a sweeping experiment. Damping was introduced in the resonance terms.

Coupled frequencies of a rotating hydroelastic shell-liquid system under zero gravity

The coupled natural frequencies of solidly rotating axially independent (two-dimensional) liquid-structure systems have been determined. The hydroelastic systems under consideration are a liquid layer around an elastic center shell, two immiscible liquids inside a cylindrical shell and an elastic shell in an infinite medium. The system was considered in a zero-gravity environment, thus being held together by surface- or interfacial tension. Strong deviation of the coupled frequencies in comparison with the uncoupled frequencies of the liquid and shell alone was found. In addition instability may occur, depending on the magnitude of the physical and geometrical parameters of the system.

Non-linear oscillations of axially independent liquid column under zero-gravity environment

For an axially independent liquid system, i.e. two immiscible liquids in a container with an interface and a liquid layer around a rigid center-core with a free liquid surface, the non-linear natural frequencies have been determined as function of the surface elevation in a zero-gravity environment. Depending on the density ratio of the two liquids and the diameter ratio of the interfaceand the container the immiscible liquid system exhibits either softening or hardening behavior, i.e. it shows with increasing interface amplitude decreasing natural frequencies or increasing natural frequency resp. For a liquid layer around a center-core the liquid oscillations exhibit a soft frequency resp. For a liquid layer around a center-core the liquid oscillations exhibit a soft backbone curve. From this one concludes that these systems, which both are in linearized theory stable, may become unstable as a consequence of large surface wave amplitudes.

Influence of the earth's gravity on measurements of the critical transport coefficients near the lambda transition of liquid helium

A review and general discussion is given of the extent to which the earth's gravitational field affects critical dynamics experiments on liquid He I near the lambda line. It is argued that the measurements of the viscosity and of the ultrasonic attenuation are not significantly affected. The measurements of the thermal conductivity will, however, definitely benefit from a zero-gravity environment. Such measurements will consitute an important test of the current theoretical understanding of lambda-point critical dynamics.

Bubble shapes in a liquid-filled rotating container under low gravity

The effect of surface tension on steady-state rotating fluids in a low-gravity environment is studied. AH values of the physical parameters used in the present calculations, except in the low-gravity environments, are based on the measurements carried out by Leslie in the low-gravity environment of a free-falling aircraft. The profile of the interface of two fluids is derived from Laplace's equation relating pressure drop across an interface to the radii of curvature that has been applied to a low-gravity rotating bubble that contacts the container boundary. The interface shape depends on the ratio of gravity to surface-tension forces, the ratio of centrifugal to surface tension forces, the contact radius of the interface to the boundary, and the contact angle. The shape of the bubble is symmetric about its equator in a zero-gravity environment. This symmetry disappears and gradually shifts to parabolic profiles as the gravity environment becomes nonzero. The location of the maximum radius of the bubble moves upward from the center of the depth toward the top boundary of the cylinder as gravity increases. The contact radius of interface to the boundary r0 at the top side of cylinder increases, and r0 at the bottom side of the cylinder decreases as the gravity environment increases from zero to 1 g.

Nonlinear liquid oscillations in spherical systems under zero-gravity

Nonlinear free oscillations of the interface of a concentric frictionless immiscible liquid system in a spherical container are investigated in a zero-gravity environment. The natural frequencies are determined for the axisymmetric and asymmetric oscillations of the interfacial surface with the diameter ratio and density ratio as parameters. It was found that for small outer- to inner liquid density ratio the oscillations exhibit softening, while for large density ratios it renders hardening oscillation. The asymmetric oscillations exhibit in the softening range softer and in the hardening range harder liquid oscillations. For a liquid layer around a rigid center sphere the oscillations of the free liquid surface yields softening behavior, where for thinner layers the softening effect is more pronounced.

Instability of rotund capillary bridges to general disturbances: Experiment and theory

Interfacial tension holds a fixed volume of incompressible fluid between coaxial circular endplates forming a capillary bridge. As the endplates are brought together very slowly the bridge fattens and eventually changes shape. In contrast to the much-studied configuration of slowly separating endplates (slender bridges), the rotund axisymmetric bridge is first unstable to nonaxisymmetric disturbances. We obtain the boundary of marginal stability (constant volume disturbances) as it depends on the aspect ratio and the volume of the bridge using an energy stability method. Furthermore, we map out the stability limit by experiment for a range of aspect ratios using neutrally buoyant fluids to simulate a zero-gravity environment. Theory and experiment are in excellent quantitative agreement and predict instability when the free interface meets each endplate tangent to its flat surface.

The influence of culture on space developments

Future space cultures may develop in living systems which could be at the level of the organization, the community, the society, or the supranational system. This article concerns all subsystem processes of such entities. For more than a quarter-century, humankind has been extending its presence successfully into outer space. The Moon landing of Apollo 11 in 1969 is changing our image of the species-we are no longer earthbound. The explorations in outer space have already begun to alter human culture on Earth, as demonstrated by the artifacts originating from space technologies. With the establishment of a more permanent presence in the higher frontier, as will happen around 1992 with the Space Station, and around 2010 with the first lunar base, humans will begin to create a new space culture as we cope with the zero-gravity environment and other aspects of living on the Moon, Mars, asteroids, and in planetary systems. To create cultural synergy in this process of human migration into space, planners should place more emphasis on the human factors involved and make greater use of the behavioral sciences, especially cultural anthropology and cross-cultural psychology, as well as a systems approach and macromanagement expertise. In our transition to a space-based culture, we should consider the development of a space deployment system for the selection and recruitment, training and orientation of those who will live for long periods in space, as well as the support services and reentry assistance to be provided the spacefarers. Systematic studies are needed on the desired characteristics to be cultivated.

Surface- and interface oscillations in an immiscible spherical visco-elastic system

The transcendental frequency equation is presented for various visco-elastic immiscible spherical liquid arrangements exhibiting free surface- and interfacial tension. The system is in a zero-gravity environment. The natural damped frequencies depend on the viscosity, surface tension, density and the Maxwell relaxation time. For a freely floating sphere the numerical results of the frequency equation are presented and exhibit with larger surface tension higher natural frequencies, for small relaxation times stronger and for larger relaxation times weaker decay of the oscillations. The increase of viscosity renders stronger decay of the oscillations. For smaller surface tension the oscillation ceases to exist and yields for small relaxation parameter τν/a2 an aperiodic motion of the drop, while for higher surface tension the oscillation of the visco-elastic sphere exhibit higher frequencies and larger decay. Increase of visco-elasticity (relaxation time) renders the begin of aperiodic motion of a liquid sphere a larger diameter. For further increased relaxation time, however, the sphere always oscillates.