Study of dynamic coefficients of water film in marine stern tube bearing considering roughness and deformation

2021 ◽  
Vol 235 (11) ◽  
pp. 2257-2271
Author(s):  
Zijun Leng ◽  
Fangrui Lv ◽  
Jianbo Zhang ◽  
Chunxiao Jiao ◽  
Gengyuan Gao ◽  
...  
Keyword(s):  
Dynamic Analysis ◽  
Water Film ◽  
Misalignment Angle ◽  
The Finite Element Method ◽  
Analysis Model ◽  
Roughness Effects ◽  
Roughness Effect ◽  
Dynamic Coefficients ◽  
Minimum Film Thickness ◽  
First Time

Dynamic analysis of water-lubricated marine stern tube bearing is incompatible with that of ordinary oil-lubricated bearing due to the deformation of compliant bushes and non-negligible roughness effects. A modified bearing dynamic analysis model embracing roughness and dynamic characteristics of a non-metal bush is proposed. Based on the model, Reynolds equations of perturbed pressures of water film considering roughness, deformation, and misalignment simultaneously are derived for the first time and solved by coupling the finite difference method and the finite-element method. The results show that dynamic coefficients are enhanced due to roughness when the minimum film thickness ratio exceeds a threshold around 2. The roughness effect is debilitated but the valid range of roughness is extended when bush deformation is considered. Additionally, dynamic coefficients of rougher bearing become obviously smaller than those of smoother bearing as the misalignment angle grows.

Roughness Effects on the Dynamic Coefficients of Ultra-Thin Gas Film in Magnetic Recording

1996 ◽  
Vol 118 (4) ◽  
pp. 774-782 ◽  
Author(s):  
Wang-Long Li ◽  
Cheng-I Weng ◽  
Chi-Chuan Hwang
Keyword(s):  
Knudsen Number ◽  
Surface Characteristics ◽  
Mean Free Path ◽  
Roughness Effects ◽  
Roughness Effect ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Induced Flow ◽  
Bearing Number ◽  
Stiffness And Damping

The stiffness and damping coefficients of a slider gas bearing operating under arbitrary Knudsen number are calculated. A perfect gas is used as the lubricant, and its behavior is described by the modified average Reynolds equation proposed by Makino et al. (1993). The effects of molecular mean free-path on the roughness-induced flow factors are included. The effects of the nondimensional film thickness, Hs0, the surface characteristics, (γ1, γ2). the inverse Knudsen number, D0, the nondimensional frequency, Ω, and the modified bearing number, Λb, on the dynamic coefficients are discussed in this paper. As expected, the values of dynamic coefficients for various roughness orientations approach the smooth value as the ratio, Hs0, becomes greater and greater, and thus the roughness effect is getting smaller and smaller. The air film of two-sided longitudinal oriented roughness is stiffer than the other two-sided oriented cases. The effect on translational damping coefficients for various two-sided oriented roughnesses is reversed as D0 greater than some value, and this value is affected significantly by Λb. Transversely rough stationary case has the lowest critical value of Λb, at which the negative translational damping appears. The results show that the roughness effect and rarefaction effect on dynamic coefficients are significant, and they cannot be ignored for stability analysis.

Dynamic Analysis of Cage Stress in Tapered Roller Bearings Using Component-Mode-Synthesis Method

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Tomoya Sakaguchi ◽  
Kazuyoshi Harada
Keyword(s):  
Rigid Body ◽  
Dynamic Analysis ◽  
Boundary Point ◽  
Axial Load ◽  
Synthesis Method ◽  
Load Condition ◽  
Component Mode Synthesis ◽  
Analysis Model ◽  
Tapered Roller ◽  
Tapered Roller Bearings

In order to investigate cage stress in tapered roller bearings, a dynamic analysis tool considering both the six degrees of freedom of motion of the rollers and cage and the elastic deformation of the cage was developed. Cage elastic deformation is equipped using a component-mode-synthesis (CMS) method. Contact forces on the elastically deforming surfaces of the cage pocket are calculated at all node points of finite-elements on it. The location and pattern of the boundary points required for the component-mode-synthesis method were examined by comparing cage stresses in a static condition of pocket forces and constraints calculated by using the finite-element and the CMS methods. These results indicated that one boundary point lying at the center on each bar is appropriate for the effective dynamic analysis model focusing on the cage stress, especially at the pocket corners of the cages, which are actually broken. A behavior measurement of a polyamide cage in a tapered roller bearing was conducted for validating the analysis model. It was confirmed in both the experiment and analysis that the cage whirled under a large axial load condition and the cage center oscillated in a small amplitude under a small axial load condition. In the analysis, the authors discussed the four models including elastic bodies having a normal eigenmode of 0, 8 or 22, and rigid-body. There were small differences among the cage center loci of the four models. These two cages having normal eigenmodes of 0 and rigid-body whirled with imperceptible fluctuations. At least approximately 8 normal eigenmodes of cages should be introduced to conduct a more accurate dynamic analysis although the effect of the number of normal eigenmodes on the stresses at the pocket corners was insignificant. From the above, it was concluded to be appropriate to introduce one boundary point lying at the center on each pocket bar of cages and approximately 8 normal eigenmodes to effectively introduce the cage elastic deformations into a dynamic analysis model.

Influence of new surface micro-structures on the performance behaviours of fluid film tilting pad thrust bearings

2021 ◽  
pp. 095440622110309
Author(s):  
JC Atwal ◽  
RK Pandey
Keyword(s):  
Mass Conservation ◽  
Performance Parameters ◽  
Algebraic Equations ◽  
The Finite Element Method ◽  
Thrust Bearings ◽  
Lubrication Equation ◽  
Tilting Pad ◽  
Minimum Film Thickness ◽  
Newton Raphson ◽  
Micro Structures

Performance parameters such as power loss, minimum film thickness, and maximum oil temperature of the sector-shaped tilting pad thrust bearings employing the new micro-structural geometries on pad surfaces have been investigated. The lubrication equation incorporating the mass-conservation issue is discretized using the finite element method and the solution of resulting algebraic equations is obtained employing a Newton-Schur method. The pad equilibrium in the analysis is established using the Newton-Raphson and Braydon methods. The influence of attributes of micro-structures such as depth, circumferential and radial positioning extents have been explored on the performance behaviours. It is found that with the new micro-structured pad surfaces, the performance parameters significantly improved in comparison to conventional plain and conventional rectangular pocketed pads.

Quality of life in adolescents and young adults with CHD is not reduced: a systematic review and meta-analysis

2015 ◽  
Vol 26 (3) ◽  
pp. 415-425 ◽  
Author(s):  
Morten Schrøder ◽  
Kirsten A. Boisen ◽  
Jesper Reimers ◽  
Grete Teilmann ◽  
Jesper Brok
Keyword(s):  
Quality Of Life ◽  
Systematic Review ◽  
Young Adults ◽  
Meta Analysis ◽  
Adolescents And Young Adults ◽  
Analysis Model ◽  
Significant Difference ◽  
Newcastle Ottawa Scale ◽  
First Time

AbstractPurposeWe performed a systematic review and meta-analysis of observational studies assessing quality of life in adolescents and young adults born with CHD compared with age-matched controls.MethodsWe carried out a systematic search of the literature published in Medline, Embase, PsychINFO, and the Cochrane Library’s Database (1990–2013); two authors independently extracted data from the included studies. We used the Newcastle–Ottawa scale for quality assessment of studies. A random effects meta-analysis model was used. Heterogeneity was assessed using the I2-test.ResultsWe included 18 studies with 1786 patients. The studies were of acceptable-to-good quality. The meta-analysis of six studies on quality of life showed no significant difference – mean difference: −1.31; 95% confidence intervals: −6.51 to +3.89, I2=90.9% – between adolescents and young adults with CHD and controls. Similar results were found in 10 studies not eligible for the meta-analysis. In subdomains, it seems that patients had reduced physical quality of life; however, social functioning was comparable or better compared with controls.ConclusionFor the first time in a meta-analysis, we have shown that quality of life in adolescents and young adults with CHD is not reduced when compared with age-matched controls.

Detailed Stress Analysis of a Spherical Acrylic Submersible by 3-D Finite Element Modeling

1999 ◽  
Author(s):  
Partha S. Das
Keyword(s):  
Finite Element ◽  
Numerical Modeling ◽  
Dissimilar Materials ◽  
Analysis Model ◽  
Element Analysis ◽  
Finite Element Analysis Model ◽  
New Model ◽  
Ocean Exploration ◽  
Near Future ◽  
First Time

Abstract Harbor Branch Oceanographic Institution (HBOI) designed, built and has operated two JOHNSON-SEA-LINK (JSL) manned submersibles for the past 25 years. The JSL submersibles each incorporate a 66–68 in. (1.6764–1.7272 m) OD, 4–5.25 in. (0.1016–0.13335 m) thick acrylic two-man sphere as a Pressure Vessel for Human Occupancy (PVHO). This type of spherical acrylic sphere or submersible was first introduced in around 1970 and is known as Naval Experimental Manned Observatory (NEMO) submersibles. As the demand increases for ocean exploration to 3000 ft. (914.4 m) depth to collect samples, to study the ocean surfaces, the problem of developing cracks at the interface of these manned acrylic submersibles following few hundred dives have become a common phenomena. This has drawn considerable attentions for reinvestigation of the spherical acrylic submersible in order to overcome this crack generation problem at the interface. Therefore, a new full-scale 3-D nonlinear FEA (Finite Element Analysis) model, similar to the spherical acrylic submersible that HBOI uses for ocean exploration, has been developed for the first time in order to simulate the structural behavior at the interface and throughout the sphere, for better understanding of the mechanical behavior. Variation of the stiffness between dissimilar materials at the interface, lower nylon gasket thickness, over designed aluminum hatch are seemed to be few of the causes for higher stresses within acrylic sphere at the nylon gasket/acrylic interface. Following the basic understanding of the stresses and relative displacements at the interface and within different parts of the submersible, various models have been developed on the basis of different shapes and thickness of nylon gaskets, openings of the acrylic sphere, hatch geometry and its materials, specifically to study their effect on the overall performance of the acrylic submersible. Finally, the new model for acrylic submersible has been developed by redesigning the top aluminum hatch and hatch ring, the sphere openings at both top and bottom, as well as the nylon gasket inserts. Altogether this new design indicates a significant improvement over the existing spherical acrylic submersible by reducing the stresses at the top gasket/acrylic interface considerably. Redesigning of the bottom penetrator plate, at present, is underway. In this paper, results from numerical modeling only are reported in details. Correlation between experimental-numerical modeling results for the new model will be reported in the near future.

Android Botnets

2021 ◽  
pp. 75-92
Author(s):  
Ahmad Karim ◽  
Victor Chang ◽  
Ahmad Firdaus
Keyword(s):  
Dynamic Analysis ◽  
High Accuracy ◽  
Remote Access ◽  
Learning Approaches ◽  
Analysis Model ◽  
Hybrid Analysis ◽  
Static And Dynamic Analysis ◽  
Mobile Botnet ◽  
Wide Scale ◽  
Access Information

Mobile botnets are gaining popularity with the expressive demand of smartphone technologies. Similarly, the majority of mobile botnets are built on a popular open source OS, e.g., Android. A mobile botnet is a network of interconnected smartphone devices intended to expand malicious activities, for example; spam generation, remote access, information theft, etc., on a wide scale. To avoid this growing hazard, various approaches are proposed to detect, highlight and mark mobile malware applications using either static or dynamic analysis. However, few approaches in the literature are discussing mobile botnet in particular. In this article, the authors have proposed a hybrid analysis framework combining static and dynamic analysis as a proof of concept, to highlight and confirm botnet phenomena in Android-based mobile applications. The validation results affirm that machine learning approaches can classify the hybrid analysis model with high accuracy rate (98%) than classifying static or dynamic individually.

Mathematic Model and Method for Solving the Heat-Exchange Problem in Electron-Beam Welding of Arbitrary Areas

2019 ◽  
Vol 291 ◽  
pp. 173-182
Author(s):  
Mykhailo Berdnyk
Keyword(s):  
Electron Beam ◽  
Electron Beam Welding ◽  
Integral Transformation ◽  
Mathematic Model ◽  
Convergent Series ◽  
Dirichlet Boundary Conditions ◽  
Temperature Fields ◽  
The Finite Element Method ◽  
Finite Space ◽  
First Time

For the first time in this article, a mathematical model has been developed for calculating the temperature fields in arbitrary areas in electron-beam welding; this model was created in the form of a boundary value problem of mathematical physics for a parabolic equation of heat conductivity with Dirichlet boundary conditions. A new integral transformation was constructed for a two-dimensional finite space, with the use of which, as well as the finite element method and Galerkin's method, a temperature field has been determined in the form of a convergent series.

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