CMES-Vol. 29, No. 2, 2008

Open Access

ARTICLE

Kinematic Analysis of Lumbar Spine Undergoing Extension and Dynamic Neural Foramina Cross Section Measurement
Yongjie Zhang¹, Boyle C. Cheng², Changho Oh¹, Jessica L. Spehar², James Burgess³
CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.2, pp. 55-62, 2008, DOI:10.3970/cmes.2008.029.055
Abstract The spinal column plays a vital biomechanical role in the human body by providing structural support and facilitating motion. As degenerative changes occur in the spine, surgical treatment may be necessary in certain instances. Such treatments seek to address pain, frequently through the restriction of spinal motion. Traditional spinal implant devices are designed to restrict the motion of a functional spinal unit (FSU) but newer device designs allow for semi-constrained motion such as spinal arthroplasty devices. In this study, a sequence of fluoroscopic imaging data was recorded during the flexibility protocol with an interspinous process spacer device placed at L2-L3.… More >

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A Boundary Element Formulation for Boundary Only Analysis of Thin Shallow Shells
E. L. Albuquerque¹, M. H. Aliabadi²
CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.2, pp. 63-74, 2008, DOI:10.3970/cmes.2008.029.063
Abstract This paper presents a boundary element formulation for the analysis of thin shallow shells. Classical plate bending and plane elasticity formulations are coupled and effects of curvature are treated as body forces. The body forces are written as a sum of approximation functions multiplied by coefficients. Domain integrals that arise in the formulation are transformed into boundary integrals by the radial integration method. Two different approximation functions are employed, that is 1 + r and r² log r. The method is applied to several problems and the accuracy of each approximation function is assessed by comparison with results from literature. More >

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Stabilized Meshless Local Petrov-Galerkin (MLPG) Method for Incompressible Viscous Fluid Flows
M. Haji Mohammadi¹
CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.2, pp. 75-94, 2008, DOI:10.3970/cmes.2008.029.075
Abstract In this paper, the truly Meshless Local Petrov-Galerkin (MLPG) method is extended for computation of steady incompressible flows, governed by the Navier--Stokes equations (NSE), in vorticity-stream function formulation. The present method is a truly meshless method based on only a number of randomly located nodes. The formulation is based on two equations including stream function Poisson equation and vorticity advection-dispersion-reaction equation (ADRE). The meshless method is based on a local weighted residual method with the Heaviside step function and quartic spline as the test functions respectively over a local subdomain. Radial basis functions (RBF) interpolation is employed in shape function… More >

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The Bauschinger Effect on 3-D SIFs for Networks of Radial and Longitudinally-Coplanar Semi-Elliptical Internal Surface Cracks In Autofrettaged Pressurized Thick-Walled Cylinders
Q. Ma¹, C. Levy², M. Perl³
CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.2, pp. 95-110, 2008, DOI:10.3970/cmes.2008.029.095
Abstract Networks of radial and longitudinally-coplanar, internal, surface cracks are typical in rifled, autofrettaged, gun barrels. In two previous papers, the separate effects of large arrays of either radial or longitudinally-coplanar semi-elliptical, internal, surface cracks in a thick-walled, cylindrical, pressure vessel under both ideal and realistic autofrettage were studied. When pressure is considered solely, radial crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factor, K_IP. Furthermore, the addition of the negative stress intensity factor (SIF), K_IA, resulting from the residual stress field due to autofrettage, whether ideal or realistic, tended to decrease… More >

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