Biodynamic Analysis of the Human Body Subjected to Vibration

Farid M. L. Amirouche fects must be accounted for in the practical considerations of Department of Mechanical Engineering comfort, performance, and safety standards. University of Illinois at Chicago AN APPROACH TO MODELING THE HUMAN BODY THE PROBLEM OF EXPOSURE TO VIBRATION DURING VIBRATION Very little is presently known about the human body's THE CONTINUING FATALITY and disability rate of vehicle mechanical behavior under various stimulus conditions. One * accident victims has motivated a number of researchers to of the most challenging problems confronting engineers study the response of the human body to impact and hightoday is the modeling of the human body. What is a good acceleration conditions. This investigation of injuries and side model? How could these models help us understand and effects resulting from the human body's exposure to lowhence prevent some classes of injuries? From one engineering intensity impact, low-acceleration, and long-term vibration, viewpoint, the human body can be looked upon as a however, has been limited. The effects of vibration on man mechanical structure, as illustrated by the use of dummies in are both physical and biological. Whole-body vibration is an the testing of crash accidents. Results obtained from those environmental condition common to all types of transportacrash tests give us a basic understanding of how a normal tion vehicles as well as to workers near heavy industrial human driver would react to such an impact. machinery. The study of vibration phenomena dates as early In the study of whole body vibration, the literature reveals as 1918, when Hamilton studied workers who used pneuthat the range of frequency for which vibration becomes matic chipping hammers and drills in the limestone quarries of harmful is between 1 and 1 5 Hz, and that resonance effects Indiana and described "spastic anemia of the hands" [1]. occur at about 4 to 5 Hz. Earlier models, such as those Vibration syndrome was described in the 1930s and 1 940s developed by Coerman, et al. [161 (see Fig. 1), used lumped by Seyring [2] who studied workers in iron foundries. Others masses to predict the human response to vibration. Actual such as Telford, et al. [31, Hunt [4], and Agate and Druett [5] experiments conducted by various researchers [8, 16-181 have studied related situations. with the lumped-mass model showed good agreement with It is believed that about 12 million workers in the United the experimental data. Later, these lumped-mass models States are affected by vibration. The possible harmful effects were improved, especially by Patil, et al. [171, along with of such vibration are, quite naturally, a matter of concern, and lead, in many cases, to permanent injury. In the past decade, there has been significant effort to develop safety measures HEAD for workers subjected to whole body vibration. Some of the results [6, 71 suggest that movements involving weak muscles are affected, especially in the case of precision work. Most experimental studies conducted on the human body [8121 contain strong medical evidence that whole-body vibraUPPER TORSO tion can cause spinal injury that results in low back pain. The response to vibration can be a determining factor in the ARM1 performance of a given task. For example, an individual SHOULDER THORAXperforming in a vibration situation may experience a feeling of SYSTEM THORAX annoyance while simultaneously sustaining a decrement in SYSTEM acuity and an increase in hand tremor [13]. Performance in an a dAI aiming task, for example, may be impaired because of these OF SPINALA,TICITY-|| (SIMPLIFIED) reactions. Most of the research reported in the literature on COLUMN human body vibration (HBV) has used sinusoidal motion to approximate the stimulus to the body. These studies [9-1221 HIPS have employed vibration platforms to produce sinusoidal vertical motions throughout specific ranges of amplitudes and r * FORCE APPLIED frequencies. However, the vibration conditions experienced TO SITTING in real life are of a random nature, with frequent impulses SUBJECT accounting for irregularities (e.g., tractor rides). ) The seriousness of the problems caused by vibration LEGS