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RESEARCH PAPERS

J Biomech Eng. 1979;101(3):157-175. doi:10.1115/1.3426241.
Abstract
Topics: Fluid mechanics
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):176-184. doi:10.1115/1.3426242.

The development of a dynamic, nonlinear finite-element model of a human leg is presented. The model is designed to accommodate large three-dimensional displacements and rotations, to accurately reflect the nonlinear stiffness characteristics of the knee joint, and to facilitate efficient stress-level calculations. Numerical examples are presented which demonstrate the nonlinear capabilities of the model. In addition, a brief example illustrates the ability of the model to respond to a complex loading history measured during a downhill skiing maneuver and to predict cross-sectional stress levels.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):185-192. doi:10.1115/1.3426243.

On the basis of data obtained from in-vitro friction tests using both cartilage and widely differing artificial surfaces, a general model for boundary lubrication of joint cartilage by synovial fluid is presented. It postulates that one portion of the synovial lubricating glycoprotein (LGP) is adsorbed to the surface. Reduction in surface shear is accomplished by formation of hydration shells about the polar portions of the adsorbed LGP creating a thin layer of viscous structured water at the surface. Mutual electrostatic repulsion between charged polysaccharide moieties aids in separation of the adsorbed surface layers. The hydration shell also serves as a check valve to control the movement of water out of and into the cartilage matrix during motion.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):193-197. doi:10.1115/1.3426244.

The elastic properties of the bone constituting human femurs have been determined from measurements of the velocities of ultrasonic compressional and shear waves through wet, embalmed bone samples. The bone has been shown to be a transversely isotropic material with the axis of symmetry parallel to the longitudinal axis of the bone. The values of the elastic constants were determined to be:

c11=6860±330 MPa E3=5500 MPa
c12=2700±570 MPa E1=4990 MPa
c13=3760±1570 MPa ν31=0.39
c33=8480±760 MPa ν12=0.20
c44=2240±180 MPa G31=2240 MPa
where the 3-axis is that of rotational symmetry and the 1- and 2-axes are in the plane of isotropy.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):198-204. doi:10.1115/1.3426245.

Numerical solutions for the steady axisymmetric flow through a disk-type prosthetic heart valve were obtained for Reynolds numbers from 50 to 600. A nonuniform mesh in both directions was used and the finite difference equations in vorticity and stream function were solved explicitly. Stream function, vorticity, and shear and normal stress plots are presented. These detailed results clearly identify regions of very high shear and normal stresses, regions of very low or very high shear stress at the walls and the extent of separated or reverse flow regions. The length of the separated flow region downstream of the disk agreed very well with experimental data. The maximum value of the shear stress occurred on the upstream corner of the disk.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):205-212. doi:10.1115/1.3426246.

A computer-based subsystem has been implemented for the smoothing and differentiation of human motion data. Nonrecursive finite impulse response digital filtering has been employed for this purpose. Filter cutoff frequency was determined using a statistical error analysis. The method of data differentiation used here is compared to other methods presented in the literature.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):213-217. doi:10.1115/1.3426247.

Populations of erythrocytes in solution were heated “instantaneously” to and maintained at temperatures in the range of 44 to 60°C on a microscope stage specifically designed for this purpose. Simultaneously, the visually observed hemolysis-time history of these cells was measured. The results were successfully correlated on the basis of two models: 1) a kinetic scheme assuming two sequential, first-order reactions by which the cells are first reversibly altered and then irreversibly damaged; and 2) a statistical model for which the number of cells that are damaged at each instant is assumed to be normally distributed. From the experimental data the rate constants for the two reactions in the kinetic model were determined and were found to have an Arrhenius dependence on temperature. By applying the statistical model to the data, we were able to determine the mean and standard deviation of the distribution curve for this model. The logarithms of these latter two parameters vary with temperature in a linear fashion.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1979;101(3):218-220. doi:10.1115/1.3426248.

The effect of the soft tissue between bone and a preloaded skin surface accelerometer was studied in vivo by comparing its output with the output of an accelerometer connected directly to the bone by a needle through the soft tissue. A 34-g skin surface accelerometer gave an output with little resemblance to the bone motions, appearing to oscillate at its resonant frequency on the soft tissue. A 1.5-g skin surface accelerometer showed nearly identical output to the bone acceleration.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J Biomech Eng. 1979;101(3):221-223. doi:10.1115/1.3426249.

Paucity of fundamental data has held back the development of stress and displacement analysis applied to the human left ventricle. Up to the present, analyses have been based on profiles dependent upon the imposition of chosen mathematical functions on single-plane radiographs. Here a process is described for a more realistic three-dimensional modelling of the geometry of the human myocardium which makes use of biplane cineangiograms. The purpose of this procedure is to provide geometric data for subsequent finite-element analysis.

Commentary by Dr. Valentin Fuster

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