A facility to perform experiments on fluid physics and specially on the mechanical behavior of liquid bridges has been designed and built. The facility consists of a velocity controlled centrifuge than can be rotated at speeds up to 10 rpm with and arm of 1.5 m where the experiment container (a Plateau tank in which different mechanical stimuli can be imposed to the liquid column) can be fixed at any location. The rotating system transmits out a video signal for diagnosis and besides control and monitoring signals are routed to the external data management system. The facility and its control system has been implemented in a way that it is possible to control and monitor the experiments either locally from a control workstation or the entire facility can enter in a mode to be controlled remotely. In this case, the control workstation is located far away the facility (indeed in a different city) and linked with data lines. The purpose of this exercise is to gain experience on the minimum data bandwidth needed and the impact on orbital platforms fluid science experimentation of transmission delays and data loses. The latter effects are implemented in the data stream in a way that can be simulated at a rate much higher than that will be experienced otherwise

Meseguer Ruiz, José

Perales Perales, José Manuel

Sanz Andres, Angel Pedro

Zayas, F.

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

  
 
 
 
 
A TELEOPERATED FACILITY FOR VARIABLE GRAVITY LEVEL 
FLUID PHYSICS EXPERIMENTATION 
 
 
F. Zayas1, J. Meseguer2, J. M. Perales2 and A. Sanz2 
 
 
1Escuela de Ingenierías Industriales, Universidad de Extremadura, E-06071 Badajoz, Spain 
2IDR/UPM, E.T.S.I. Aeronáuticos, Universidad Politécnica de Madrid, E-28040 Madrid, Spain  
 
 
 
ABSTRACT 
 
A facility to perform experiments on fluid physics and specially on the mechanical behavior of liquid bridges has 
been designed and built. The facility consists of a velocity controlled centrifuge than can be rotated at speeds up to 
10 rpm with and arm of 1.5 m where the experiment container (a Plateau tank in which different mechanical stimuli 
can be imposed to the liquid column) can be fixed at any location. The rotating system transmits out a video signal 
for diagnosis and besides control and monitoring signals are routed to the external data management system. The 
facility and its control system has been implemented in a way that it is possible to control and monitor the 
experiments either locally from a control workstation or the entire facility can enter in a mode to be controlled 
remotely. In this case, the control workstation is located far away the facility (indeed in a different city) and linked 
with data lines. The purpose of this exercise is to gain experience on the minimum data bandwidth needed and the 
impact on orbital platforms fluid science experimentation of transmission delays and data loses. The latter effects 
are implemented in the data stream in a way that can be simulated at a rate much higher than that will be 
experienced otherwise. 
 
 
INTRODUCTION 
 
Liquid bridges occur in both natural and technological situations and have been studied for practical reasons and 
for basic scientific interest. In the simplest configuration a bridge consists of an isothermal drop of liquid held by 
surface tension forces between two parallel solid disks, as shown in Figure 1.  
 
Disregarding additional electric and magnetic fields effects, the equilibrium interface shape of such a liquid bridge 
configuration is determined by the following dimensionless parameters: 
• The slenderness, Λ=L/(2R), where L is the distance between the supporting disks and R = (R1+R2)/2 is the mean 
radius.  
• The ratio of the radius of the smaller disk to the radius of the larger one, K = R1/R2.  
• The dimensionless eccentricity, e = E/R, 2E being the distance between the disk axes.  
• The dimensionless volume, V=V*/(πR2L) defined as the ratio of the actual volume V* to the volume of a 
cylinder of the same length L and diameter R.  
• The Bond number B =∆ρaR2/σ, where ∆ρ is the difference between the density of the liquid and the density of 
the surrounding medium and a is the acceleration acting on the liquid (whose axial and lateral components are 
aa = acosα and al = asinα, respectively). 
 
The behavior, either static or dynamic, of a liquid bridge depends on the values of the above mentioned geometrical 
and volume dimensionless parameters as well as on the nature of the imposed perturbation (Bond number or other 
stimuli). Equilibrium shapes and stability limits of capillary liquid bridges have been investigated theoretically and 
  
experimentally for some time, and there is an extensive body of literature dealing with such fluid configurations 
(Meseguer et al., 1994, Meseguer et al., 1999). 
 
Most of the published papers deal with liquid bridges 
subjected to small Bond numbers. Since B=DraR2/s, it 
can be made small by reducing the acceleration a acting 
on the liquid column. This can be achieved in a free fall 
experiment (for example in a drop tower, on aircraft 
flying parabolic flight trajectories, in sounding rockets 
and on low-earth orbit platforms). The Bond number 
can also be reduced by matching the densities of the 
working liquid and the surrounding fluid (the Plateau or 
neutral buoyancy technique) or by using supporting 
disks with very small radius (micro or millimetric liquid 
bridges). 
 
In the experimental facility described in the following 
the three aforementioned effects that contribute to the 
magnitude of the Bond number can be, within limits, 
independently controlled. In this facility, the neutral 
buoyancy technique is employed and Dr is controlled 
by selecting the appropriate density of the surrounding 
fluid. Support disks of different diameters can be also 
used and the liquid column is mounted on a centrifuge 
so that the magnitude of the acceleration acting on the 
bridge can be adjusted by varying the rotation rate of 
the centrifuge. The accelerations to be accounted for are gravity, g, plus the centripetal one due to the solid-body 
rotation of the liquid bridge, Ω2r, so that a = (g2+Ω4r2)1/2. 
 
It must be pointed out that the Bond number is not constant along the liquid column. This is because the liquid 
bridge rotates as a solid body and the centripetal acceleration varies with the distance to the rotation axis. However, 
for particular conditions the effect of the Bond number gradient can be negligible (Zayas et al., 2000).  
 
APPARATUS 
 
The experimental facility, as sketched in Figure 2, consists of a liquid bridge cell mounted on a horizontal, rotating 
platform. The platform can rotate at any prescribed angular velocity within the range 0-1.05 rad.s−1 (0-10 rpm) with 
an accuracy of ±2×10−3 rad.s−1 (±0.02 rpm). The rotating platform is a metallic beam 1.5 m in radius (A), mounted 
on a support structure (B) where the electric motor used to rotate the beam as well as the control electronics are 
located (C). 
 
The rotating platform (A) supports the test box (D)  as well as the data and commands transmission unit (E), which 
is located at the platform rotation axis. The test box 
consists of two rectangular plates with a hinge mounted 
Fig. 1.  Liquid bridge sketch showing relevant 
parameters 
 
Fig. 2.  Sk
  D 
 
  
 
 
y 
x 
Fr 
z 
0 
Upper disk Aon a common side (as sketched in the insert in Figure 
2). One of the plates (D1) is attached to the rotating 
platform whereas the second one (D2) can be rotated at 
any prescribed angle with respect to D1. Presently, both 
etch of th
 D2 B
the position of the plate D1 along the rotating arm and 
the angle between plates D1 and D2 are set manually 
(so that the rotation must be stopped to change these 
e expe
D1 CErimentalL/2L/2 EERR fLower diskpositions), although a new test box in which these 
position can be changed without stopping the rotating 
arm is now under development. 
 
acility 
  
Upper plate D2 supports the liquid bridge cell (LBC), the illumination system, a video camera to record the 
experiments, a set of batteries to power supply for the recording and illumination system, and a set of small 
containers with the fluids for the liquid bridge and the surrounding bath. To perform the experiments the so called 
neutral buoyancy or Plateau technique is used: the liquid column is formed inside another liquid (surrounding bath) 
of nearly the same density but immiscible with the former. Usually a dimethyl-silicone oil is used as the working 
liquid whereas for the surrounding bath a mixture of methanol and distilled water is used (since LBC test chamber 
is tight, no alcohol evaporation occurs, so that the surrounding bath density is constant). 
 
Several liquid bridge cells have been developed. The simplest liquid bridge cell is a tight chamber connected to a 
calibrated syringe. In this case the LBC test chamber is a 0.04m×0.04m×0.04m aluminium cube, with two opposite 
faces made of a transparent, plastic material. This allows visualization of the liquid bridge. The liquid bridge is 
formed between two equal disks 0.01 m in diameter. One of the disks is connected to the piston of the syringe and 
can be displaced along its axis by using a micrometer screw. The remaining disk is fixed to the opposite side of the 
test chamber such that both disks remain in coaxial alignment whatever their separation distance. Liquid is injected 
and removed, using quick-disconnect valves, from the liquid bridge through a hole in the centre of the moving disk 
which connects it with the syringe. The diameter of the piston is equal to the diameter of the disks and the moving 
disk is mounted at one end of the piston syringe. Thus, the amount of liquid injected or removed when the disk is 
displaced causes the volume of the liquid column to be cylindrical within 0.1 % accuracy (V = (1±0.001)2πΛ) 
regardless of the distance separating the disks. 
 
There are three different small containers in the system for fluids supply and disposal: one of them is used to supply 
the fluid to form the liquid bridge; the second one is used to supply the surrounding bath; and the third is used to 
recover the fluids from inside the test cell when occasionally the liquid bridge is broken in the experimentation 
process. 
 
Observation system 
 
To monitor the system performance an 8 mm CCD video camera video is used (Figure 3), together with a TV 
sender and a TV receiver. The video camera is installed in the platform that supports the test cell, with the optical 
axis aligned with the centre of the observation window, and  the video output from the camera is connected to a 
small and low power TV emitter, located in the axis of the rotation arm. Omnidirectional antennae are used in the 
emitter and TV receiver in order to minimise the signal modulation caused by the rotation of the TV station inside 
the laboratory and, also, both pieces of equipment are battery powered. 
 
 
 
 
Fig. 3.  Observation system schematics
 
Control System 
 
The system has been devised to allow an easy change of mode of co
troubleshooting and debugging purposed) to remote (for analysing the imp
transmission delays in experiment performance and scientific return). 
 
The different analogue signals coming from or going to the rotating table a
converter, and the video signal coming from the sender on board the rotatin
frame grabber. Both the data acquisition board and the frame grabber are in 
software running on it (based in LabView). The inputs/outputs of the contro
socket. This allows for an easy connection to the Man Machine Interface (MM
t 
Test cell and camera  TV receiver and control se
TV sender 
e Attached to the rotating arm 
n
iLocated in a remote sittrol from local (for setting-up and 
act of data bandwidth reduction and 
re digitised by an analogue to digital 
g table is received and digitised by a 
nstalled in a PC and controlled by the 
l software are redirected to a TCP/IP 
I) which also sends and receives data 
  
via the same TCP/IP socket, so that the MMI software can run on the very same machine where the controller 
resides (this mode is used only for troubleshooting), in a machine next to the controller or remotely, without any 
change (Figure 4). The design also allows the introduction of random delays (just using the Internet as a transport 
system) or controlled delays by inserting a module to receive the TCP/IP packets and store them in a buffer for a 
while. 
 
When the MMI is run in a PC close to the facility, a LAN is used, but for remote communications either the 
Internet or a dedicated ISDN connection can be used. If the Internet is used, bandwidth can oscillate widely, whilst 
the ISDN allows for a constant but reduced bandwidth. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
CONCLUSIONS 
 
A experimental facility for fluid science experimentation has been developed and a control system for it has been 
devised that allows easy operation either locally or remotely. The purpose of the remote control is to evaluate the 
impact on operations and scientific performance of the delays and reduced bandwidth of communications. The 
development is in the frame of preparing future operations of the experimental facilities on board the International 
Space Station. One of the experiment operation modes will be to interface with the experiment directly from the 
experimenter laboratory (User Home Base, UHB) connected with a data line (ISDN type) with the ground 
operations infrastructure. Obviously, the impact of this reduced bandwidth on operations directly from UHBs must 
be exercised before the actual experiment to evaluate the need of better communications or of operating the 
experiment directly from a centre with dedicated and better data lines (the so called Facility Responsible Centres, 
FRCs, and Facility Support Centres, FSCs. 
 
ACKNOWLEDGEMENTS 
 
This work has been supported by the Spanish Comisión Interministerial de Ciencia y Tecnología (CICYT), and 
also by the European Community under the FEDER funded project 1FD1997-1669/ESP. 
 
REFERENCES 
 
Meseguer, J., N.A. Bezdenejnykh and P. Rodríguez de Francisco, On the Use of Liquid Bridges as Accelerometers, 
Microgravity Sci. Technol., 9, 62, 1996. 
Meseguer, J., J.M. Perales, I. Martínez, N.A. Bezdenejnykh, and A. Sanz, Hydrostatic Instabilities in Floating Zone 
Crystal Growth Process, Current Topics in Crystal Growth Res., 5, 27, 1999. 
Meseguer, J., L.A. Slobozhanin and J.M. Perales, A Review on the Stability of Liquid Bridges, Adv. Space Res., 
16, 5, 1994. 
Zayas, F., J.I.D. Alexander, J. Meseguer and J.-F. Ramus, On the Stability Limits of Long Non-Axisymmetric 
Cylindrical Liquid Bridges, Phys. Fluids, 12, 979, 2000. 
Fig. 4.  Block diagram of the control system 
Frame 
Grabber 
 
CCD
Communications 
Software 
ISDN or Internet 
Man Machine 
Interface 
Experimental 
Facility 
Sender Receiver 
Rotating 
table 
Local Controller Remote Controller 
Controlling 
Software 
A/D 
D/A 
Converter
Communications 
Software 


A teleoperated facility for variable gravity level fluid physics experimentation

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