Effect of Clearance on Rotary Rock Bit Journal Bearing Contact Stress

1986 ◽  
Vol 108 (1) ◽  
pp. 1-7 ◽  
Author(s):  
K. M. Marshek ◽  
H. H. Chen
Keyword(s):  
Numerical Method ◽  
Large Scale ◽  
High Stress ◽  
Design Tool ◽  
Linear System Of Equations ◽  
High Stress Concentration ◽  
Pressure Area ◽  
Bit Life ◽  
Rock Bit ◽  
Conformal Contact

This paper presents a numerical method for analyzing the effect of clearance on closely conforming rotary rock bit journal bearings. The modified Boussinesq point-force displacement influence function and the modified profile function are introduced in conjunction with the discretization of the integral equation. Automatic mesh generation is employed to redefine a new pressure area boundary and therefore round-off errors normally found while solving a large-scale linear system of equations can be avoided. The numerical method has been implemented in a computer program and has been applied to the problems of misaligned and perfectly aligned conformal contact. There is a close agreement with the Persson’s analytical solution at the center of the aligned bearing length. However, owing to a high stress concentration at the bearing edge, the edge pressure distribution will differ significantly from the Persson’s plane stress model. The conformal contact will have a comparatively higher peak pressure and lower contact-angle than the Hertzian line contact prediction. The results of the analysis provides a design tool for improving drill bit life.

scholarly journals Toward a method for downscaling sea ice pressure

2020 ◽  
Author(s):  
Jean-Francois Lemieux ◽  
Bruno Tremblay ◽  
Mathieu Plante
Keyword(s):  
High Pressure ◽  
Sea Ice ◽  
Numerical Experiments ◽  
Large Scale ◽  
High Stress ◽  
Small Scale ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
High Stress Concentration ◽  
Ice Pressure

Abstract. Sea ice pressure poses great risk for navigation; it can lead to ship besetting and damages. Contemporary large-scale sea ice forecasting systems can predict the evolution of sea ice pressure. There is, however, a mismatch between the spatial resolution of these systems (a few km) and the typical dimensions of ships (a few tens of m) navigating in ice-covered regions. In this paper, we investigate the downscaling of sea ice pressure from the km-scale to scales relevant for ships. Results show that sub-grid scale pressure values can be significantly larger than the large-scale pressure (up to $\\sim$ 4x larger in our numerical experiments). High pressure at the sub-grid scale is associated with the presence of defects (e.g. a lead). Numerical experiments show that a ship creates its own high stress concentration by forming a lead in its wake while navigating. These results also highlight the difficulty of forecasting the small-scale distribution of pressure and especially the largest values. Indeed, this distribution strongly depends on variables that are not well constrained: the rheology parameters and the small-scale structure of sea ice thickness (more importantly the length of the lead behind the ship).

Localized Autofrettage as a Design Tool for the Fatigue Improvement of Cross-Bored Cylinders

1998 ◽  
Vol 120 (4) ◽  
pp. 393-397 ◽  
Author(s):  
A. E. Segall ◽  
C. Tricou ◽  
M. Evanko ◽  
J. C. Conway
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
High Stress ◽  
Circular Crack ◽  
Design Tool ◽  
Element Analysis ◽  
High Stress Concentration ◽  
Significant Extension ◽  
The Cross ◽  
Machining Operations

An investigation was launched into the feasibility of improving the fatigue life of thick-walled cylinders with cross-bores by using a localized autofrettage technique. This technique utilized the high stress concentration at the cross-bore to induce localized residual stresses using relatively low internal pressures. An elastic-plastic finite-element analysis indicated that the resulting residual stresses in the vicinity of the cross-bore were predominately compressive and not sufficient in magnitude to induce reverse plasticity. When the resulting residual stresses were used with an elastic fracture-mechanics assessment of a quarter-circular crack at the intersection of the cylinder and cross-bore inner diameter, a significant extension of fatigue life was shown to be possible. In addition to prolonging the useful life of the cylinder, the localized residual stresses were shown to be possible at pressures below the yield threshold for the thick-walled cylinder. Thus, reverse plasticity, permanent deformations, and the need for post-autofrettage machining operations that could inadvertently lessen the beneficial results of a traditional autofrettage were avoided.

Integrity Assessment and On-Site Repair of a Floating Production Platform

2005 ◽  
Author(s):  
Mauro G. Marinho ◽  
Alexandre M. Pope ◽  
Luiz Claudio Meniconi ◽  
Luiz Henrique M. Alves ◽  
Cesar Del Vecchio
Keyword(s):  
High Stress ◽  
Local Strain ◽  
Business Unit ◽  
Gusset Plates ◽  
Strain Measurements ◽  
Integrity Assessment ◽  
High Stress Concentration ◽  
Production Platform ◽  
Welding Defects ◽  
Classification Society

Following the warning of a flooded bow horizontal brace of a semi-submersible production platform, an inspection diving team was mobilized and cracks were found at both bow and aft K-joints. Analysis of the service life of the platform, together with the results of structural analysis and local strain measurements, concluded that cracking was caused by fatigue initiated at high stress concentration points on the gusset plates inserted in the tubular joints. As a consequence of the fractured plates other cracks were nucleated close to the intersection lines of the braces that compose the K-joints. Based on this analysis different repair possibilities were proposed. To comply with the production goals of the Business Unit it was decided to repair the platform on-site and in production in agreement with the Classification Society. The proposed repair contemplated the installation of two flanges on the gusset plates between the diagonal braces by underwater wet (UWW) welding. Cracks at the gusset plates were also removed by grinding and wet welding. Defects located at the braces are being monitored and repaired by the installation of backing bars, by wet welding, followed by grinding and welding from the inside. To carry out the job two weld procedures and ten welder-divers were qualified.

An Experimental Study of Cavity Nucleation During Superplastic Deformation

1990 ◽  
Vol 196 ◽  
Author(s):  
Jiang Xinggang ◽  
Cui Jianzhong ◽  
Ma Longxiang
Keyword(s):  
Grain Boundary ◽  
Superplastic Deformation ◽  
Thermomechanical Processing ◽  
High Stress ◽  
High Strength ◽  
Optical Microscope ◽  
Grain Boundary Sliding ◽  
Cavity Nucleation ◽  
High Stress Concentration ◽  
Voltage Electron

ABSTRACTCavity nucleation during superplastic deformation of a high strength aluminium alloy has been studied using a high voltage electron microscope and an optical microscope. The results show that cavities nucleation is due only to superplastic deformation and not to pre-existing microvoids which may be introduced during thermomechanical processing. The main reason for cavity nucleation is the high stress concentration at discontinuties in the plane of the grain boundary due to grain boundary sliding.

A New Shaft Coupling Design for a High-Speed Rotor Wheel

1995 ◽  
Author(s):  
Tibor Kiss ◽  
Wing-Fai Ng ◽  
Larry D. Mitchell
Keyword(s):  
High Speed ◽  
High Stress ◽  
Critical Issue ◽  
Working Environment ◽  
Outer Diameter ◽  
Stress Concentrations ◽  
Coupling Region ◽  
Rotor Wheel ◽  
High Stress Concentration ◽  
Safety Margins

Abstract A high-speed rotor wheel for a wind-tunnel experiment has been designed. The rotor wheel was similar to one in an axial turbine, except that slender bars replaced the blades. The main parameters of the rotor wheel were an outer diameter of 10“, a maximum rotational speed of 24,000 RPM and a maximum transferred torque of 64 lb-ft. Due to the working environment, the rotor had to be designed with high safety margins. The coupling of the rotor wheel with the shaft was found to be the most critical issue, because of the high stress concentration factors associated with the conventional coupling methods. The efforts to reduce the stress concentrations resulted in an advanced coupling design which is the main subject of the present paper. This new design was a special key coupling in which six dowel pins were used for keys. The key slots, now pin-grooves, were placed in bosses on the inner surface of the hub. The hub of the rotor wheel was relatively long, which allowed for applying the coupling near the end faces of the hub, that is, away from the highly loaded centerplane. The long hub resulted in low radial expansion in the coupling region. Therefore, solid contact between the shaft and the hub could be maintained for all working conditions. To develop and verify the design ideas, stress and deformation analyses were carried out using quasi-two-dimensional finite element models. An overall safety factor of 3.7 resulted. The rotor has been built and successfully accelerated over the design speed in a spin test pit.

The Influence of Switch Temperature on Coke Drum Fatigue Life

2010 ◽  
Author(s):  
Fa´bio de Castro Marangone ◽  
Ediberto Bastos Tinoco ◽  
Carlos Eduardo Simo˜es Gomes
Keyword(s):  
Fatigue Life ◽  
Structural Model ◽  
High Stress ◽  
Axial Direction ◽  
Pressure Vessels ◽  
High Stress Concentration ◽  
Short Period ◽  
Bending Stresses ◽  
Switch Temperature ◽  
Lower Temperature

Coke drums are thin-walled pressure vessels that experience severe thermal cycling condition which consists of heating, filling and rapidly cooling the drum in a short period of time. After some years under operation, cracks at the vessel may occur, especially at high stress concentration areas such as the skirt support to shell attachment. During the filling phase of the cycle, when the empty and cooled coke drum is filled with hot oil, the shell and cone temperatures increase rapidly compared to the skirt temperature and the last is pushed outward, since its bottom is at lower temperature and fixed at a concrete base. During quenching (sudden cooling) phase, the coke drum is filled with water at about 80°C and tends to cool faster than the skirt, which is pulled inward until equilibrium is obtained. The skirt expansion and contraction movement results in bending stresses in axial direction on the top of skirt. As lower the switch temperature is, more severe is the bending effect. One of PETROBRAS delayed coke unit presented some operational problems at pre-heating phase, resulting in lower switch temperatures. This paper presents an analysis showing the influence of the switch temperature on coke drum fatigue life. At first, the transient loading conditions were established from thermocouple measurements at skirt attachment weld (hot box region). Later, a transient thermal analysis was performed with FEA and the temperature gradient at the skirt attachment during entire thermal cycle was obtained. The thermal results were then converted to a structural model which was solved for linear elastic stress including other loads such as pressure. Finally, the maximum stress components for both filling and quenching phases were determined and a complete stress range was calculated as per ASME Section VIII, Div 2. The procedure described above was applied for different switch temperatures scenarios in order to show its influence on the fatigue life of the coke drum.

scholarly journals Mental health disorders among students from rural areas three months after returning to school: a cross-sectional study among Polish students (12-13 y.o.)

2022 ◽  
Author(s):  
Piotr Długosz
Keyword(s):  
Mental Health ◽  
Rural Areas ◽  
Large Scale ◽  
Negative Impact ◽  
Positive Impact ◽  
High Stress ◽  
Mental Health Disorders ◽  
Mental Condition ◽  
Health Disorders ◽  
Returning To School

Abstract: Background: All over the world, the negative impact of the Covid-19 pandemic on children and adolescents’ mental health is observed. The conducted research aims to verify whether returning to schools, to the education inside the classroom in the company of their peers, improved or undermined the students’ mental health. Metods: The study was carried out on a sample of students inhabiting rural areas in a borderland region. The research sample was collected using purposive sampling and consisted of 552 respondents from 7th and 8th grades of primary school. An auditorium questionnaire was used to gather the research material. Results: Three months after returning to school, the students are in a bad mental condition. 61% of the respondents are satisfied with their lives, 52% of the respondents show symptoms of depression measured with the WHO-5 index, whereas 85% of them have average and high stress levels as measured with the PSSC scale. Higher levels of mental disorders was observed among females, the students inhabiting villages and evaluating their financial status as worse. Conclusions: Returning to schools failed to have a positive impact on the students’ mental health. Disorders occurring at a large scale will have a negative influence on the students’ performance and hinder their re-adaptation to school. Educational authorities shall immediately provide the students with support and monitor the situation in the next months.

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