492
Abstracts
most noticeable changes occurred at the proximal and distal levels. At the proximal level, the strains (stresses) were reduced and in some cases reversed from that of the intact joint. At the most distal level the strains were increased, particularly with the insertion of a long-stem prosthesis. These tests suggest that the normal load transmitting function of the tibia1 bone undergoes redistribution after total knee arthroplasty. Clinically this could result in bone resorption and/or remodelling and the possible loosening of the prosthesis. F.
MODELLING
A STRAIN ENERGY FUNaION
FOR A GUINEA PIG GALLBLADDER
N. GUZELSU (L. S. U. Medical Center, Dept. of Orthopaedics,
LA)
A theoretical model is given for the elastic response of a Guinea pig gallbladder in its passive state. It is assumed that the gallbladder is incompressible, homogeneous and isotropic. The experimental points, which are obtained by the simple tension experiment, of the gallbladder rings in different positions and orientations support the above assumptions. The experimental points of rings, under the simple tension, (axial load vs stretch) in a semilogarithmic scale suggest that an exponential type strain energy function with two physical constants (strain energy function is only the function of the second strain invariant) can adequately describe the mechanical behavior of a Guinea pig gallbladder. This work implies that the experimental curves in semi-logarithmic scales (load vs stretch) can be used for choosing the simplest exponential type strain energy function for biological tissues. AN ANALYSIS OF SOFT TISSUE LOADING
IN THE FOOT
ROY D. CROWNINSHIELD and SACHIO NAKAMURA(Biomechanics Laboratory, Orthopaedic Surgery, University of Iowa, Iowa City, IA)
Department
of
During the performance of everyday activity, the foot is subjected to repeated loading which, in many cases, represents constant trauma and misuse. The biomechanical behavior of the foot is, at present, not well understood. In particular, the magnitudes of stresses developed within the plantar skin during foot function and the dependency of these magnitudes on shoe design is not well-known. This presentation reports on a planar. large displacement and nonlinear finite element stress analysis of the foot within a shoe. The foot is modelled with a bony skeleton and plantar region of thick skin. An experimental determination of skin material properties revealed a highly nonlinear and nearly incompressible behavior. The elastic properties of the shoe sole are represented in the model by a variety of both linear and nonlinear materials. Shoe soles were considered with regard to their effect on the resulting stress developed within the plantar skin. ENHASCED
DIFFUSION IN LUSG GAS MIXING
H. D. VAN LIEW and D. J. WILKINSON(Department of Physiology, State University of New York at Buffalo, Buffalo. NY) Our goal was to discover whether convective processes, during inspiration and during the disturbances caused by each heart beat, have a significant effect on gas mixing in the lung. We compared experimental results obtained with subjects in a hyperbaric environment, in which mixing is poorer than normal, with predictions from our computer model which simulates gas diffusion in a lung-shaped vessel. The results show that the model simulations will correspond to the experimental data only if input for either diffusivity or time for diffusion is much larger than the true values. We conclude that molecular diffusion is enhanced, by a factor of about 6, by convective processes in the lung. (Supported in part by NHLBI Grant POl-HL-14414
and ONR Contract NOOO14-76-000471).
MASS TRANSPORT TO PULSATILE FLOWS IN CIRCULAR TUBES GIVE\
CUR\‘.ATL’RE I\
\ ARIOC’S
DIFFERENT PATTERNS
P. D. RICHARDSON, P. M. GALLETTI(Brown University, Providence, Rhode Island, U.S.A.) and K. TANISHITA(Tokyo Women’s Medical College, Tokyo, Japan) Mass transport through the tube-walls is enhanced when the tubes are curved instead of straight Analysis of the flow [e.g. F. T. SMITH (1975) JournalofFIuid Mechnnics 71,151 has concentrated on helical curvature where the radius remains constant. Biomedical application of curved tube devices (e.g. implantable artificial lungs may use tubes given curvature in various patterns. Mass transfer has been measured in rirro using both water and blood with
Abstracts tubes
in helical, serpentine,
Patterns: steady flow with was used as the pulsatile flow. The mass transfer coefficients for O2 and CO, show that with all of these curvature patterns and for the range of Dean and Womersley numbers involved, the transport is correlated best with the magnitude of the oscillatory velocity, and that in a tubing enhanced transport, the pattern ofcurvature is less important than curvature itself; repeated reverses of curvature as in woven patterns do not cancel the benefits of curvature. superimposed
forward
493
and reverse spiral and woven
(macrame)
simple harmonic oscillations (various amplitudes and frequencies)
ON PARACHUTIST DYNAMICS ROKALD
L. HUSTOX and JAMES W. KAMMAK (University
Results of a computer simulation and a configurations prior to ‘opening shock’, are particularly, the head/neck system dynamics minimize the subsequent force and moment discussed. Application in parachute design
of Cincinnati,
Cincinnati,
OH)
parameter study are presented. A variety of initial parachutist considered and the relative effects on the parachutist’s dynamics - are studied. Optimal initial (pre-opening) configurations. which pulses experienced by the head/neck system, are identified and and in developing jumping strategies is also discussed.
RESPOYSE OF A SIMPLIFIED INTERVERTEBRAL DISC MODEL USDER COMPLEX LOADI\G
R. L. SPILKER and D. M. DAUGIRDA (Department of Materials Engineering, Illinois at Chicago Circle, Chicago, IL)
University
of
A simplified axisymmetric finite-element model of the vertebral body-intervertebral disc is described which employs three homogeneous substructures corresponding to the vertebral body/endpIate region, the annulus fibrosis of the intervertebral disc, and the nucleus pulposis. The first two regions are modelled as istropic materials with the vertebral body/endplate region treated as nearly rigid compared with the annulus. The nucleus is modelled as an incompressible, inviscid fluid. The response of the model to compression, torsional. shear, and moment loadings is examined. A Fourier series representation of circumferential behavior allows the analysis to be reduced to a 2-dimensional model for each loading case. The model is used to examine the effects ofgross disc geometry and material property parameters on predicted intradiscal pressure increase. disc bulge, and other pertinent displacement quantities. The results obtained indicate that all parameters have a significant effect on disc displacements. Only compressive loading produces increases in intradiscal pressure, and these pressure increases are most strongly affected by changes in disc height and radius. For torsional and moment loading, predicted displacements are shown to correlate reasonably with strength of materials solutions. Results obtained with this simplified model are also shown to be in reasonable agreement with published experimental measurements, with appropriate choice ofmaterial property parameters. MASS DENSITY DISTRIBUTlON ALONG THE BODY AXIS
H. K. Ht ANG, PETER WEISS, D. D. ROBERTSONand F. R. SCAREZ (Department Physiology Kc Biophysics, Georgetown University Medical School, Washington,
of D.C.)
The purpose of this paper is to report on data of the distribution of various physical properties along the body axis. This data was generated using the computerized tomographic scanning technique, Five cadaveric specimens, ranging in age from a newborn infant to a 7-yr old child, have been studied usmg this method. Each specimen was scanned from the head to the ankle joints at 1 cm increments, Each CT scan produces a cross-sectional image of the body cross-section under consideration. The CT image can then be related to the mass density distribution ofthe scanned section. Using standard picture processing techniques and formulae for discrete masses in mechanics. the mass, area, specific gravtty. geometrical center. center of gravity. and inertia tensor for each cross-section are estimated. For each parameter, the sectional quantity the parameter along the body. (This research
is supported
by NHTSA,
vs the body axis can be plotted,
Department
of Transportation.
demonstrating
Contract
SIJCCESS I\
of
No. DOT-HS-7-01661.)
H. K. Huan8 cr nl.. Utilization of CT Scans as Input to Finite Elements Analysis Proc Intern Biomechanrcs. Feb. 18-20, 1980, pp 797-816. IYFLUENCE OF THREE-DIMENSIONAL GEOMETRY ON
the disrributlon
Finite Elements In
THE BENCH PRESS
N. MADSEX (Department of Mechanical Engineering) and T. MCLAUGHLIN (National Strength Research Center, Interdisciplinary Biomechanics Laboratory. Auburn University. Auburn, AL) In recent years the increased incidence of musculoskeletal injuries in the population due to bench presses served as motivation for detailed analysis of this motion. Kinematic 2-D studies of 13 1 world-class and beginner subjects