A Dynamics-Based Fidelity Assessment of Partial Gravity Gait Simulation Using Underwater Body Segment Ballasting

Abstract

In-water testing is frequently used to simulate reduced gravity for quasi-static tasks.For dynamic motions, however, the assumption has been that drag effects invalidate any data, and in-water testing has been dismissed in favor of complex and restrictive techniques such as counterweight suspension and parabolic flight. In this study, motion-capture was used to estimate treadmill gait metrics for three environments:underwater and ballasted to 1 g and to 1/6th g, and on dry land at 1 g. Ballast was distributed anthropometrically. Motion-capture results were compared with those for a simulated dynamic walker/runner, and used to assess the effect of the in-water environment on simulation fidelity. For each test case, the model was tuned to the subject's anthropometry, and stride length, pendulum frequency, and hip displacement were computed. In-water environmental effects were found to be sufficiently quantifiable to justify using in-water testing, under certain conditions, to study partial-gravity gait dynamics.

An instrumented centrifuge for studying mouse locomotion and behaviour under hypergravity

“…hypergravity). One of the oldest techniques for simulating reduced gravity for astronaut training has been to submerge the subject in a tank of water, using ballast to vary their buoyancy and hence their effective weight (Trout and Bruchey, 1969; Mirvis and Akin, 2011); the main disadvantage of this technique is hydrodynamic effects such as drag. A similar technique is to enclose the lower half of the subject's body in a pressurised chamber (Grabowski, 2010; Saxena and Granot, 2011), although this only exerts an upwards force on the portion of the body enclosed by the device.…”

Design and analysis of an active gimbal simulator with three degrees-of-freedom for ground testing

“…To reconstruct the translational and rotational motions of the satellites and spacecraft in outer space on the ground, the micro-G environment and full degrees-of-freedom (DOFs) are required. Various methods have been proposed such as parabolic flight, 5 neutral buoyancy, 6,7 air-bearing, 8,9 hardwarein-the-loop, 10,11 and suspension systems. 3,4 The parabolic flight method 5 uses an aircraft to simulate the parabolic motion and is the standard of fidelity.…”

“…However, this approach only allows a very short time (approximately 20 s) and limited space. The neutral buoyancy 6,7 method is difficult to access and expensive to operate because of its sealing requirements. Moreover, this method is always limited to the study of quasi-static tasks such as training astronauts, because of the viscous drag.…”