Satish B Shenoy

Steady state characteristics of misaligned multiple axial groove water-lubricated journal bearing

This paper deals with the influence of misalignment on the static performance of bearings having three axial grooves that are equi-spaced in the circumferential direction. The lubricant (water) is supplied from one end of the bearing that flows both in axial and circumferential direction and exits from its other end. Effects of misalignment in both vertical and horizontal plane are numerically computed for groove angles 36° and 18° using the modified Reynolds equation and finite difference method. The influence of misalignment on the steady state characteristics such as load capacity, friction coefficient, and side leakage is analyzed for both the groove angles with different eccentricity ratios. The load capacity and the side leakage flow, which is slightly more for bearing with groove angle 18° when compared with 36° groove angle, increases with the degree of misalignment (DM). The friction coefficient is less for bearing with groove angle 18°, when compared with bearing with 36° groove angle. The friction coefficient decreases with increase in DM for vertical misalignment for both the bearings.

Effect of intrusive and retraction forces in labial and lingual orthodontics: A finite element study

Objectives: Lingual orthodontics differs in biomechanics as compared to labial system and has biomechanical advantages. Although theoretical approaches have explained the differences between labial and lingual orthodontics, the finite element method (FEM) may be better suited to analyze these differences. This study analyzes the effect of vertical and horizontal forces together on the tooth using FEM. Materials and Methods: An extracted right maxillary central incisor was radiographed and was used to create a solid model using ANSYS. The geometric model was converted into a finite element model with the help of ANSYS software. The model consists of 27,000 elements and 30,000 nodes. Two force vectors (vertical and horizontal) were applied labially and lingually at 3 different heights- 4 mm, 5 mm and 6 mm from the incisal edge. Results: In the labial system, the net force vector passes through the center of resistance (CR) and brings about intrusion. The net force vector in lingual orthodontics does not pass through the center of resistance and produces lingual tipping of the incisors. Conclusion: Intrusion and retraction forces bring about tipping of incisors in lingual orthodontics. The same amount of intrusion and retraction forces brings about intrusion of incisors in labial orthodontics. Therefore, direction and amount of forces should be carefully and judiciously applied after taking into consideration the resultant biomechanical differences.

Static characteristics of misaligned multiple axial groove water-lubricated bearing in the turbulent regime

The static characteristics of misaligned three-axial water-lubricated journal bearing in the turbulent regime are analyzed for groove angles 36° and 18°. Ng and Pan’s turbulence model is applied to study the turbulence effects in the journal bearing. The static parameters such as load-carrying capacity, friction coefficient, and side leakage are found for different degree of misalignment (DM). The change in flow regime of the lubricant from laminar to turbulent and the increase in misalignment, improved the load capacity of the bearing. For lightly loaded bearings, the friction coefficient of the bearing increased with the increase in Reynolds number.

Dynamic characteristics of a single pad externally adjustable fluid film bearing

Purpose – The paper aims to devise an externally adjustable fluid film bearing whereby the hydrodynamic conditions can be changed as required in a controlled manner. Unlike a tilting pad bearing, in this bearing film thickness can be varied by providing radial and tilt adjustments to the pad, irrespective of the operating conditions. This variation in film thickness in‐turn varies the stiffness and damping coefficients.Design/methodology/approach – The stability characteristics of a centrally loaded 120° single pad externally adjustable fluid film bearing is studied theoretically. The bearing has an aspect ratio of one and operates over a wide range of eccentricity ratios and adjustments. The time dependent form of Reynolds equation in two dimensions is solved numerically using the finite difference method. Dynamic performance characteristics of the bearing are in terms of film stiffness and damping coefficients, critical mass of the journal and the whirl frequency ratio. Stability is determined using a f...

Evaluation of Lingual Orthodontic appliances

Due to increasing popularity of lingual orthodontics in recent years, various lingual systems have been developed. In orthodontics Finite Element Method (FEM) has been used to study various types of tooth movement. Although FEM was extensively used for evaluating the biomechanical effects of labial orthodontic forces, research on lingual system is still limited. The purpose of this study is to evaluate the efficacy of two different lingual bracket systems using FEM. FEM of maxilla which included six upper anterior teeth, periodontal ligament has been created. Six upper anterior teeth were digitally arranged in final position using a new computerized method. CAD models of six upper anterior brackets of 7 generation and Lingual matrix have also been created and attached onto the digital model at appropriate heights. Various orthodontic movements were simulated and force applied distal to the canine bracket. Deformation, stress on teeth, bone and periodontal ligament were studied and compared between the two different lingual systems. Deformation was less with lingual matrix brackets than 7 generation brackets when subjected to intrusive, retractive and combined forces. More stresses were generated on the teeth, bone and PDL in lingual matrix brackets than 7 generation brackets when subjected to forces. It was found that tooth movements are more efficient and precise in lingual matrix brackets than prefabricated 7 generation brackets.

A comparative study of forces in labial and lingual orthodontics using finite element method

Background: Orthodontic treatment requires optimum force to achieve desirable tooth movement with minimal damage to the root, periodontal ligament (PDL), and alveolar bone. Hence, quantifying the magnitude and direction of force is very important for orthodontic treatment. Both labial orthodontics (LaO) and lingual orthodontics (LiO) are used for orthodontic tooth movements, which differ considerably in their biomechanics. Although these differences have been explained, force magnitude need to be evaluated. Aims: 1. To evaluate the differences in biomechanics of tipping movement in LaO and LiO using finite element method (FEM). 2. To quantify the reduced amount of force in LiO as compared LaO in tipping. Study Settings: It is a computational tool where three-dimensional (3D) FEM models of upper incisor is simulated in order to map and compare the stress produced by tipping movement performed with lingual and LaO. Materials and Methods: A 3D FEM model of the maxillary right central incisor was made from a geometric model. A 50 g tipping force was applied on a labial side. The principal stress patterns in the PDL for orthodontic tooth movement were recorded. When 50 g of tipping force was applied from a lingual side, higher stress values were observed. The forces on the lingual side were reduced to 45 g, 40 g, 35 g, 34 g, 33.5 g, and 33 g to check the maximum stress pattern on PDL. Results: A 50 g tipping force applied on the labial side will bring about 0.0252 N/mm 2 maximum principal stress. When the same amount of force applied on the lingual side will bring about 0.0375 N/mm 2 maximum principal stress. A 33.6-g force applied on the lingual side will bring about 0.0252 N/mm 2 maximum principal stress which is similar to 50 g of force applied on the lingual side. Conclusion: A palatally directed tipping force of 33.6 g in LiO was sufficient for orthodontic tooth movement. Tipping in LiO required 32.8% less force when compared to LaO.