DYNAMICS OF HUMAN BODY EXPOSED TO LOW-FREQUENCY VIBRATION DURING SPACEFLIGHT

Abstract

The future crewed space mission involves expeditions and settlements on the other planets and making space accessible to ordinary people. The vibration intensity during the dynamic phases of spaceflight is expected to rise in future launch vehicles. The elevated vibration level would have an unfavorable impact on the human body and deteriorates physical and psychological performance. Presently, the vibration limits to the crew during the pre-flight and dynamic phases of spaceflight are recommended as per ISO 2631-1, which are applicable only to vibration transmitted to the human body in seated, standing, and recumbent posture. Most of the existing literature on the human body studied the effects of vibration in the eyeballs up/down (head-to-foot) direction. In contrast, the spaceflight crew experience the vibration in the eyeballs in/out (chest-to-back) condition. Only a handful of studies deal with the influence of whole-body vibration on humans in semi-supine (eyeballs in / out) posture. It may be as this posture is not common in regular modes of transportation or military vehicles. In order to protect the crew from the harmful effect of vibration, the dynamic behavior of the human body in such an environment needs better understanding. Therefore, the thesis is aimed to investigate the influence of low-frequency vibration on the human body in a semi-supine posture condition and provides insight into human biodynamics and subjective responses. A 3D finite element (FE) model of the semi-supine human body is developed initially to determine its principal vibrational modes and gain knowledge of the human body dynamics. The human body is modeled based on anthropometric measurement of 50th percentile Indian male, where each body segment is represented by an ellipsoidal segment with homogeneous material properties. The natural frequencies and mode shapes have been obtained through the modal analysis. The principal vibration mode for the semi-supine human body has been observed at 9.44 Hz in the vertical direction, at 8.22 Hz in the longitudinal direction, and 4.21 Hz in the lateral direction. It is also observed that the principal vertical mode involves significant vertical movement of the upper body segments and primarily concentrated in the lower torso, which may cause pain in the lumbar spine.