Circumferential Contact Research Articles

Proposition of Helical Thread Modeling with Accurate Geometry and Finite Element Analysis

Distinctive mechanical behaviors of bolted joints are caused by the helical shape of thread geometry. Recently, a number of papers have been published to elucidate the strength or loosening phenomena of bolted joints using three-dimensional finite element analysis. In most cases, mesh generations of the bolted joints are implemented with the help of sophisticated commercial software. Therefore, the mesh patterns thus obtained are not necessarily adequate for analyzing the stress concentration and contact pressure distributions, which are the primary concerns when designing bolted joints. In this paper, an effective mesh generation scheme is proposed, which can provide helical thread models with accurate geometry in order to analyze such important characteristics as the stress distribution along the helix and the contact pressure distributions on the pressure flank. Using the FE models constructed according to the proposed procedure, it is shown how the thread root stress and contact pressure vary along the helix. Also shown is how the imperfect engagement of the mating threads, around the top and bearing surfaces of the nut, affects the circumferential contact pressure distribution at the nut loaded surface and the axial load distribution along engaged threads.

Use of intracardiac ultrasound to guide balloon catheter cryoablation of the left atrial-pulmonary venous junction: Determinants of ablation efficacy

Background: Cryothermy is attractive for use in AF ablation because of its favorable safety profile, but the “heat load” associated with PV blood flow makes traditional catheter designs less effective. A balloon cryoablation catheter (BC) placed at the PV ostia may circumvent this limitation since 1) circumferential contact may be maximized and 2) the negative thermal effects of ambient blood flow may be attenuated. This study evaluates these concepts using a BC prototype in early clinical experience using intracardiac ultrasound (ICE) to guide balloon positioning.

Nerve Regeneration after Modified End-to-Side Neurorrhaphy in the Rat

Purpose: The aim of this study was to evaluate the effect of modified end-to-side neurorrhaphy on functional recovery, by modulating the epineurial window and contact areas with a donor nerve, using a rat median nerve and finger flexors. Materials and Methods: Four experimental groups (n=10) were used: a large epineurial window and a spiral circumferential contact with the donor nerve (Group A): a large epineurial window and half a contact with the donor nerve (Group B): a small epineurial window and half a contact with the donor nerve (Group C): and a nontransferred control (Group D). Grasping testing, muscle contractility testing, and a histological study were performed. Results: Twenty weeks after surgery, the grasping strength, tetanic force and nerve fiber count were significantly higher in group A than group C. The modified end-to-side repair can enhance axonal sprouting from an intact nerve, and improve functional recovery. Conclusion: Either the epineurial window surface area or the contact configuration with the donor nerve is an important factor in an end-to-side coaptation model.

Blue and Cartis sever relations

The present work deals with practical consequences of non-point character of circumferential contacts on samples tested using van der Pauw (vdP) method. Apart from the measurement method itself, the fundamental paper of van der Pauw deals also with an estimate of the error due to contact of finite length at the circumference of a circular sample on assumption of equipotential contact region. In general, this is true only in case of vanishing contact resistivity. The present study discusses the consequences of non-fulfilment of this assumption in practice and demonstrates it on real samples made from thin copper foil. The circumferential contact surfaces on these samples are made of the same material and the same thickness as measured sample. It was shown that, in principle, there is no experimental error in the resistivity measurements caused by finite size of contact surfaces. This is a consequence of the trivial fact that the contact surfaces modify only the shape of the sample, which – in the sense of the vdP methodology – can be arbitrary. This conclusion can be further generalised as follows. A non-point contact of lower resistivity than the measured sample results in negative measurement error, whereas the contact of higher resistivity results in positive error. So the magnitude and sign of the error depends not only on the relation between the contact length and sample diameter but also on the relation between the resistivities of the contact and the sample.

Power Doppler Ultrasonography for the Assessment of Vascular Invasion by Pancreatic Cancer

Aim: To investigate the diagnostic accuracy of power Doppler ultrasonography (US) in assessing the vascular invasion by pancreatic cancer. Methods: A prospective study of 40 consecutive patients with pancreatic cancer (head 35, body 5) was performed. All patients underwent surgery. The relationships between tumor and each vessel were classified into four types according to the closest circumferential contact of the tumor with the vessel. A type 0 indicated no contact; type 1 indicated less than one third contact; type 2 indicated one third to 99% contact, and type 3 indicated encasement. Vascular invasion was diagnosed in types 2 and 3. The diagnostic accuracy was evaluated in the portal vein and in the splanchnic arteries (celiac artery, common hepatic artery, and superior mesenteric artery). The power Doppler US findings were confirmed by the operative findings. The results of power Doppler US were compared with those of CT scan and angiography. Results: Portal vein invasion was confirmed in resected specimens in 23 cases and by operative findings in 5 cases. For the diagnosis of portal vein invasion, sensitivity, specificity, and overall accuracy of power Doppler US were, respectively, 79.3, 90.9, and 82.5%. The respective values were 79.3, 100, and 85% for CT and 72.4, 81.8, and 75% for angiography. For the diagnosis of arterial invasion, sensitivity, specificity, and overall accuracy of power Doppler US were 80, 92, and 90%, respectively. The corresponding values were 47, 88, and 73% for CT and 47, 100, and 80% for angiography. Conclusion: Power Doppler US proved to be useful for the diagnosis of vascular invasion by pancreatic cancer.

AN EFFICIENT CRANKSHAFT DYNAMIC ANALYSIS USING SUBSTRUCTURING WITH RITZ VECTORS

A structural analysis using dynamic substructuring with Ritz vectors is presented for predicting the dynamic response of an engine crankshaft, based on the finite-element method. A two-level dynamic substructuring is performed using a set of load-dependent Ritz vectors. The rotating crankshaft is properly coupled with the non-rotating, compliant engine block. The block compliance is represented by a distributed linear elastic foundation at each main bearing location. The stiffness of the elastic foundation can be different in the vertical and horizontal planes, thereby considering the anisotropy of the engine block compliance with respect to the crankshaft rotation. The analysis accounts for the kinematic non-linearity resulting from the crankangle-dependent circumferential contact location between each journal and the corresponding bore of the engine block. Crankshaft “bent” and block “misboring” effects due to manufacturing imperfections are considered in the analysis. The superior accuracy and reduced computational effort of the present method as compared with the equivalent superelement analysis in MSC/NASTRAN, are demonstrated using the free and forced vibrations of a slender cylindrical beam and free vibrations of a four-cylinder engine crankshaft. Subsequently, the accuracy of the present method in calculating the dynamic response of engine crankshafts is shown through comparisons between the analytical predictions and experimental results for the torsional vibrations of an in-line five cylinder engine and the bending vibrations of the crankshaft-flywheel assembly of a V6 engine.

Assessment of Resectability of Pancreatic Head and Periampullary Tumors by Color Flow Doppler Sonography

To examine the sensitivity of color flow Doppler ultrasonography in assessing resectability of pancreatic head and periampullary tumors. Validation cohort study. Tertiary care public hospital. Thirty-seven patients with pancreatic head or periampullary cancer were studied by color flow Doppler examination of the relevant blood vessels. A pancreatic Doppler score (PDS) was defined as the closest circumferential contact of the tumor to the superior mesenteric vein, superior mesenteric artery, or portal vein. A PDS of 1 indicated no contact (n = 9); PDS 2, less than 50% contact (n = 10); PDS 3, 50% to 99% contact (n = 7); and PDS 4, encasement (n = 11). The PDS was compared with operative and histologic resection margins. The lack of vascular invasion was confirmed operatively in 7 of 7 patients with a PDS of 1, and 6 patients who underwent resection had clear histologic margins. Nine (90%) of 10 patients with a PDS of 2 were confirmed to have no vascular invasion, and 3 (43%) of 7 patients who underwent resection had clear margins. Five (83%) of 6 patients with a PDS of 3 had correct operative findings, and both patients who underwent resection had positive margins. Operative confirmation of encasement was found in all 7 patients with a PDS of 4 who had operative exploration, and none underwent resection. Color flow Doppler sonography and PDS predicted resectability and the histologic margin status (positive predictive value, 97%). Patients with a PDS of 1 are predicted to have clear histologic margins after resection. Patients with a PDS of 4 have unresectable tumors, and nonoperative palliation should be considered. Patients with a PDS of 2 or 3 have a high likelihood of positive histologic margins after resection and may be candidates for neoadjuvant chemotherapy.

Natural Frequencies of Stator Core with Frame in Induction Motor.

The construction and the frame with a fin in a totally enclosed induction motor have almost the same design worldwide. A method for estimating natural frequencies of a stator core pressed into the frame of this type of motor was found by a finite-element method (FEM) analysis. First, the number of circumferential contact points between the inner surface of the frame and the outer surface of the core was determined by experiments and FEM analysis. It was confirmed that the number of circumferential contact points was three. In these analysis, spring elements with radial and circumferential spring constants were set at these contact points. Good agreement in natural frequencies obtained by measurement and by FEM analysis was attained when the number of spring constants in the radial direction was infinite and that in the circumferential direction was finite. FEM analysis with spring elements at contact points is useful in practical applications to obtain the natural frequencics of a stator core with frame.

Polymorphonuclear leukocytes occlude capillaries following middle cerebral artery occlusion and reperfusion in baboons.

Microvascular perfusion defects may accompany sustained occlusion and subsequent reperfusion of the middle cerebral artery; however, the nature of such "no-reflow" defects remains unclear. In the absence of antithrombotic pretreatment, we documented lenticulostriatal microvascular flow integrity following 3-hour middle cerebral artery occlusion and 1-hour reperfusion in a baboon occlusion/reperfusion model by two methods identifying 1) microvascular occlusion and 2) microvascular patency. Microvascular "no-reflow" involved capillaries (vessels of 4.0-7.5 microns diameter) of the lenticulostriatal territory. Capillary reflow included 27-39% of all capaillaries in two subjects, indicating a significant reduction of perfusion from normal (2p = 0.045). In identical experimental preparations, single polymorphonuclear leukocytes completely occluded 4.7% of microvessels of capillary diameter in randomly selected fields, partially occluded 3.5% of postcapillary venules, and occluded 40% (four of 10) of capillaries in linear reconstruction along a 110 microns length. Circumferential contact between polymorphonuclear leukocytes and the luminal endothelial cell membranes was documented, with an intrecellular gap of, at most, 160 nm. Fibrin was found with degranulated platelets when the latter were associated with granulocytes, but not with polymorphonuclear leukocytes alone. The finding of capillary-obstructing polymorphonuclear leukocytes in the microvascular bed following middle cerebral artery reperfusion in focal ischemia in this model satisfies an essential requirement for postulating their role in early microvascular injury and the "no-reflow" phenomenon.

ROOT AERATION IN UNSATURATED SOIL: A MULTI‐SHELLED MATHEMATICAL MODEL OF OXYGEN DIFFUSION AND DISTRIBUTION WITH AND WITHOUT SECTORAL WET‐SOIL BLOCKING OF THE DIFFUSION PATH

SummaryTreating the root as a homogeneous cylinder with respect to oxygen diffusivity and respiratory demand is a mathematically convenient assumption that has long been an inherent weakness and potential source of error in modelling the oxygen relations of soil‐aerated roots. The two models described here render such assumptions unnecessary: radial differences in oxygen diffusivity and respiratory demand between stele, cortex, wall layers and rhizosphere film have been accommodated by modelling the root: rhizosphere system as a multicylindrical unit. The models were designed to examine the influence of radial and circumferential cortical gas‐phase diffusion on oxygen concentrations and, also, to supplement recent theoretical studies into the effects of a sectoral blocking of the radial diffusion path for oxygen by circumferential contact between root and wet soil. Model I treats symmetrical surroundings assuming uniformity in the rhizosphere and accommodates the formation of an anoxic region within the root. Model II allows for the probability of partial blocking of the root's circumference, but only holds for fully aerobic roots.As expected the results reveal markedly contrasting oxygen profiles between those roots having significant cortical gas‐phase diffusion (porous roots) and those without such diffusion (non‐porous). A stepped oxygen profile, the result of a shallow gradient in the cortex, characterizes the porous roots; in non‐porous roots a smooth profile is predicted. It is also predicted that as a consequence of cortical gas‐phase diffusion the maximum oxygen deficit (MOD) in porous roots ought normally to be confined to the stele and, with a deterioration in the soil oxygen supply, the stele will be first to experience anoxia. More adverse conditions accompany a high level of circumferential blocking and a second anoxic zone (in a part of the wall) should arise prior to the development of more widespread anoxia. In the examples shown, extensive blocking was required to create some stelar anoxia in porous roots but the apparent resistance to diffusion in the wall layer(s) and rhizosphere film in the unblocked sector was greatly enhanced by the effects of blocking elsewhere. It is shown that in the partially blocked porous root oxygen should mostly move circumferentially in the cortex of the blocked sector; movement in the stele should be largely radial. In non‐porous roots, blocking quickly shifts the MOD to the wall layers adjoining the blockage centre and the examples chosen indicated a wedge of anoxia spreading from the wall into cortex and stele when blocking exceeded 20%. Wall thickness was however of no particular significance. Annular contours, which indicate radial transport, are quickly lost as blocking progresses around non‐porous roots and eventually transport is approximately unidirectional across most of the root.

The Circumferential Contact Problem for the Belted Radial Passenger Car Tire

SUMMARY The belted radial passenger car tire is idealized as a prestressed circular ring connected to a hub through a distribution of linear springs modeling the sidewall. A second distribution of such springs exterior to the ring represents the tread rubber. The tire is supposed to be at rest, loaded at its hub, and pressed onto a flat, rigid, frictiontess roadway. In this situation the linear differential equations of the model are solved using a singular perturbation technique. Given the load at the hub, the solutions furnish the length of tread in contact with the road, the radial and circumferential displacement of all points on the ring, and the distribution of pressure over the region of contact.

Singular Perturbation Solutions of the Circumferential Contact Problem for the Belted Radial Truck and Bus Tire

Singular Perturbation Solutions of the Circumferential Contact Problem for the Belted Radial Truck and Bus Tire

The Circumferential Contact Problem for the Belted Radial Tire

The Circumferential Contact Problem for the Belted Radial Tire