Journal Bearing Design Types And Their Applications To Turbomachinery.

Tutorialpg. 179-190A review of several different types of hydrodynamic journal bearings that are commonly found in turbomachinery is presented. Emphasis is placed on the key geometric design parameters of each type. The discussion covers plain journal, axial groove, pressure dam, offset split, lemon bore, multilobe and titling-pad bearings. The application of the critical speed map and some basic non-dimensional bearing parameters as tools for preliminary bearing selection and comparison are discussed. These tools are applied to two case studies, which demonstrate the proper application of different bearing designs to industrial turbomachinery

A rare case of abdominal cocoon

Abdominal cocoon is a rare cause of intestinal obstruction usually diagnosed incidentally at laparotomy. It mani- fests by forming a membrane that typically encases the small bowel loops, leading to mechanical obstruction. Preoperative diagnosis is difficult. The etiology of this condition is not well understood; however, it is a form of chronic irritation and inflammation. METHOD: A 33 years old male, from Bangladesh, presented to our emergency department complaining of abdominal pain, nausea, and vomiting. CT abdomen shows a picture of intestinal obstruction at the level of the small intestine. Intraoperative findings showed encapsulation of small bowel by a dense whitish membrane as a cocoon. Histological exam- ination showed a granulomatous peritonitis and Ascaris Lumbricoides in the bowel resected. RESULTS AND CONCLUSIONS: The preoperative diagnosis of abdominal cocoon is difficult and hence, the diagnosis is usu- ally confirmed by laparotomy. Surgery remains the cornerstone in the management of abdominal cocoon. The pathogen- esis of abdominal cocoon remains elusive and has been associated with several conditions. The initial diagnosis of our patient was bowel obstruction from cocoon syndrome (CT and intraoperative findings) probably primitive, and only his- tologically proved granulomatous peritonitis associated with the presence of the parasite

Rotor Dynamic Analysis And Bearing Optimization Study Of A 3800 Hp Steam Turbine

PaperPg. 19-27.This paper presents the highlights of a complete rotor dynamics analysis and bearing optimization study that was performed on a 3800 HP multistage steam turbine. This unit is coupled to a three stage, poster-type, centrifugal air compressor with two high speed pinion shafts engaging a common bull gear. The turbine drives the lower speed pinion at a maximum speed of 10,500 rpm. Located at the other end of this same pinion is the first stage impeller wheel. The second and third stages are mounted on the higher speed pinion, rotating at a maximum speed of 13,600 rpm. The maximum speed of the bull gear is 1, 940 rpm. All the existing compressor bearings are the four-lobe type. The original turbine rotor consists of three stages and has a 41.34 inch bearing span. The bearings are lemon-bore type with journal diameters of 3.0 and 4.0 inches on the inlet and exhaust ends, respectively. This turbine has exhibited subsynchronous vibration, at approximately half rotational speed, during field testing. The half frequency vibration prevented operation above 9,400 rpm because a shaft resonance was excited and vibration levels became prohibitively high. The analysis of the existing rotor-bearing system predicts that the turbine operates close to the second critical speed and that the rotor is stable under normal load conditions. However, the rotor becomes unstable when the lemon-bore bearings are unloaded. There are two major sources of bearing load in addition to gravity. These loads are misalignment and gear mesh loading. Misalignment can result from differential thermal growth of the turbine and compressor cases and supports. If the coupling does not act as an ideal joint, this differential growth can impose external loads at the bearings. The bearing load resulting from the gear mesh is a reaction to the torque transmission at the gear interface. For example, the turbine driver rotates in the counter-clockwise direction. Therefore, the low speed pinion gear tends to climb up the bull gear, which causes an upward external load on the pinion bearings. As in the case of misalignment, if the coupling is not ideal, the turbine bearings can also be affected by these gear mesh reaction loads. This analysis is primarily concerned with the effect of these external loads that oppose gravity and cause degrees of net bearing unloading because the unloading causes rotor instability. The rotor is unstable with 75 pounds unloading at each bearing or 110 pounds unloading at the exhaust end bearing alone (with a normal gravity load at the inlet end bearing). As a solution to the problem, a new set of bearings was designed to stabilize the rotor and move the peak response speeds away from the operating speed range. The new bearings are five-shoe-tilt-pad bearings with load-between-pad orientation. The inlet end bearing has a 3.0 inch diameter bore with length-to-diameter ratio of 1.0; and preload of 0.8. The exhaust end bearing has a 3. 995 inch diameter bore with a length-to-diameter ratio of 0.4 and preload of 0.0. With the new tilt-pad bearing design there are no response peaks in the normal operating speed range and the system log decrement is 2.8 times higher than with the existing system, under normal load conditions. The log decrement for the tilt-pad bearings is +0.52 for an unloading of 100 pounds. Therefore, the tilt-pads provide a stable rotor support that is not sensitive to unloading

Validation of an electrogoniometry system as a measure of knee kinematics during activities of daily living

Purpose: The increasing use of electrogoniometry (ELG) in clinical research requires the validation of different instrumentation. The purpose of this investigation was to examine the concurrent validity of an ELG system during activities of daily living. Methods: Ten asymptomatic participants gave informed consent to participate. A Biometrics SG150 electrogoniometer was directly compared to a 12 camera three dimensional motion analysis system during walking, stair ascent, stair descent, sit to stand, and stand to sit activities for the measurement of the right knee angle. Analysis of validity was undertaken by linear regression. Standard error of estimate (SEE), standardised SEE (SSEE), and Pearson’s correlation coefficient r were computed for paired trials between systems for each functional activity. Results: The 95% confidence interval of SEE was reasonable between systems across walking (LCI = 2.43 °; UCI = 2.91 °), stair ascent (LCI = 2.09 °; UCI = 2.42 °), stair descent (LCI = 1.79 °; UCI = 2.10 °), sit to stand (LCI = 1.22 °; UCI = 1.41 °), and stand to sit (LCI = 1.17 °; UCI = 1.34 °). Pearson’s correlation coefficient r across walking (LCI = 0.983; UCI = 0.990), stair ascent (LCI = 0.995; UCI = 0.997), stair descent (LCI = 0.995; UCI = 0.997), sit to stand (LCI = 0.998; UCI = 0.999), and stand to sit (LCI = 0.996; UCI = 0.997) was indicative of a strong linear relationship between systems. Conclusion: ELG is a valid method of measuring the knee angle during activities representative of daily living. The range is within that suggested to be acceptable for the clinical evaluation of patients with musculoskeletal conditions

Role of dopamine–adenosine interactions in the brain circuitry regulating effort-related decision making: insights into pathological aspects of motivation

Brain dopamine, particularly in the nucleus accumbens, has been implicated in activational aspects of motivation and effort-related processes. Accumbens dopamine depletions reduce the tendency of rats to work for food, and alter effort-related decision making, but leave aspects of food motivation such as appetite intact. Recent evidence indicates that the purine neuromodulator adenosine, largely through actions on adenosine A2A receptors, also participates in regulating effort-related processes. Adenosine A2A antagonists can reverse the effects of dopamine D2 antagonists on effort-related choice, and intra- accumbens injections of adenosine A2A agonists produce effects that are similar to those induced by accumbens dopamine depletion or antagonism. These studies have implications for the understanding and treatment of energy-related disorders such as anergia and fatigue in psychiatry and neurology

Dynamic Analysis Of An 8000 HP Steam Turbine Operating Near Its Second Critical Speed.

LecturePg. 79-92A rotordynamics analysis of an 8000 hp steam turbine which drives an ethylene compressor is presented. This machine characteristically exhibited increasing vibration levels with increasing speed, in the upper portion of the speed range. It was suspected that this ramping vibration was due to operation near a critical speed. The purpose of this analysis was to identify the source of this high vibration with the present rotor and hearings and then to determine the best solution to the problem. The computer analysis determined that the original rotor/bearing system was operating near the second critical speed. The predicted peaks were within nine percent to thirteen percent of miming speed (8400 cpm). The optimum solution was to shorten the shaft at the governor end and replace the bearings. The shaft modification consisted of cutting off the governor worm gear assembly and replacing it with an electronic governor disk. This new bearing design was also a four-shoe tilting pad journal bearing, but it had longer pads and higher preload than the existing design. Because there was concern about coupling gear tooth lock-up in the original design, a dry, flexible-element coupling design was evaluated. The coupling change was also of interest because of its potential effect on moving the second critical speed. However, in this ease, the analysis determined that the rotor vibration characteristics were very close with either the existing gear coupling or the dry coupling. Therefore, the justification fo r changing couplings would be that the dry coupling would not be susceptible to drive tooth lockup and unbalance eccentricity due to tooth wear

Rotor Dynamics Modification Of An Eight Stage Compressor For Safety/Reliability Improvement.

LecturePg. 81-96The catastrophic failure of a high pressure centrifugal air compressor utilizing air-pressurized bearing housings dictated the redesign of its sister compressor. The modification of this early 1950's compressor involved elements of both practical and analytical design. The project included the design of new bearings and seals and the alteration of various support systems to permit operation with non-pressurized bearing housings. The project was undertaken as risk minimization, with all performance and reliability improvements being additional benefits. The matching of the computer model with the field data of the existing system was the key to its successful evaluation. It was found that a case seal was acting as an additional bearing during certain operating conditions. This third bearing caused the compressor to behave differently than had been predicted with the initial two-bearing models. With the system properly modeled, changes were proposed to optimize the rotor dynamics. The main objectives were to achieve reliable rotor dynamic characteristics and to maintain the integrity of the process labyrinth seals. The changes were made in April, 1982, with the normal hardware fitting considerations. The subsequent start-up and operation were without incident. The modified compressor has performed well through a number of emergency trips and subsequent restarts, exhibiting exceptional rotor stability and overall reliability

Impact of Caffeine on Ethanol-Induced Stimulation and Sensitization: Changes in ERK and DARPP-32 Phosphorylation in Nucleus Accumbens

Background: Caffeine is frequently consumed with ethanol to reduce the impairing effects induced by ethanol, including psychomotor slowing or incoordination. Both drugs modulate dopamine (DA)-related markers in accumbens (Acb), and Acb DA is involved in voluntary locomotion and locomotor sensitization. The present study determined whether caffeine can affect locomotion induced by acute and repeated ethanol administration in adult male CD-1 mice. Methods: Acute administration of caffeine (7.5 to 30.0 mg/kg) was evaluated for its effects on acute ethanol-induced (1.5 to 3.5 g/kg) changes in open-field horizontal locomotion, supported rearing, and rearing not supported by the wall. DA receptor-dependent phosphorylation markers were assessed: extracellular signal-regulated kinase (pERK), and dopamine-and cAMP-regulated phosphoprotein Mr32kDa phosphorylated at threonine 75 site (pDARPP-32-Thr75) in Acb core and shell. Acutely administered caffeine was also evaluated in ethanol-sensitized (1.5 g/kg) mice. Results: Acute ethanol decreased both types of rearing. Caffeine increased supported rearing but did not block ethanol -induced decreases in rearing. Both substances increased horizontal locomotion in a biphasic manner, and caffeine potentiated ethanol-induced locomotion. Although ethanol administered repeatedly induced sensitization of locomotion and unsupported rearing, acute administration of caffeine to ethanol-sensitized mice in an ethanol-free state resulted in blunted stimulant effects compared with those seen in ethanol-naïve mice. Ethanol increased pERK immunoreactivity in both subregions of the Acb, but coadministration with caffeine blunted this increase. There were no effects on pDARPP-32(Thr75) immunoreactivity. Conclusions: The present results demonstrated that, after the first administration, caffeine potentiated the stimulating actions of ethanol, but did not counteract its suppressant or ataxic effects. Moreover, our results show that caffeine has less activating effects in ethanol-sensitized animals

Bupropion Increases Selection of High Effort Activity in Rats Tested on a Progressive Ratio/Chow Feeding Choice Procedure: Implications for Treatment of Effort-Related Motivational Symptoms

Background: Depression and related disorders are characterized by deficits in behavioral activation, exertion of effort, and other psychomotor/motivational dysfunctions. Depressed patients show alterations in effort-related decision making and a bias towards selection of low effort activities. It has been suggested that animal tests of effort-related decision making could be useful as models of motivational dysfunctions seen in psychopathology. Methods: Because clinical studies have suggested that inhibition of catecholamine uptake may be a useful strategy for treatment of effort-related motivational symptoms, the present research assessed the ability of bupropion to increase work output in rats responding on a test of effort-related decision-making (ie, a progressive ratio/chow feeding choice task). With this task, rats can choose between working for a preferred food (high-carbohydrate pellets) by lever pressing on a progressive ratio schedule vs obtaining a less preferred laboratory chow that is freely available in the chamber. Results: Bupropion (10.0–40.0 mg/kg intraperitoneal) significantly increased all measures of progressive ratio lever pressing, but decreased chow intake. These effects were greatest in animals with low baseline levels of work output on the progressive ratio schedule. Because accumbens dopamine is implicated in effort-related processes, the effects of bupropion on markers of accumbens dopamine transmission were examined. Bupropion elevated extracellular dopamine levels in accumbens core as measured by microdialysis and increased phosphorylated dopamine and cyclic-AMP related phosphoprotein 32 kDaltons (pDARPP-32) immunoreactivity in a manner consistent with D1 and D2 receptor stimulation. Conclusion: The ability of bupropion to increase exertion of effort in instrumental behavior may have implications for the pathophysiology and treatment of effort-related motivational symptoms in humans