Case Study 08: Torsional Oscillation Trouble on VFD Motor Driven Recip Compressor

Case StudyHigh vibration problems including failed coupling parts on a VFD motor driven reciprocating compressor are analyzed and the root causes and solutions are discussed in this costly field issue

The Baffling And Temperature Prediction Of Coupling Enclosures.

LecturePg. 115-124Increasingly, turbomachinery users are setting upper limits on coupling enclosure temperatures. This is done either to protect personnel, to ensure the proper operating temperature for bearing oil that leaks past seals (or is intentionally drained through the coupling guard), and/or to ensure coupling instrumentation (e.g., torquemeter) temperature limits are not exceeded. Computer programs and formulas that have previously been developed to predict the temperature rise are not necessarily accurate in some cases. This is because much of the work is based on limited configurations in laboratory experiments. There has also been a lack of direct correlation with "real" situations, as guards are not normally instrumented for temperature measurement. Work is presented that has been done on actual applications at the Marathon Oil Refinery, and at Elliott Company's facilities, and in other field installations to correlate test data with predicted temperatures using the existing programs. Moreover, proper guard and coupling designs will be discussed, especially those that prevent the vacuum effect that sucks oil past machinery seals. Finally, actual field problems and solutions are covered

Is The Dry Coupling Really Causing Your Vibration Problem?

LecturePg. 129-143From time to time vibration probes pick up high vibration at the coupling location on output shafts. Many times the coupling will then be removed and sent to the shop or to the manufacturer for inspection, repair, and rebalancing. In many of these cases, especially with dry couplings, however, the root cause is elsewhere [1]. The coupling vibration-and sometimes damage can be a symptom of other problems in the train. What these vibrations mean is addressed as related to the coupling and vibration signature. Is it the coupling, or is the rotor out of balance? Or, is there a problem with the fit between the two? What else could be wrong? Field cases are presented where suspected coupling problems turned out to be something entirely different. In one case, an axially vibrating coupling turned out to be the result of a resonance condition in the feedback loop in the controller of a variable frequency motor. This resonance caused a torsional vibration that showed up axially in the coupling. In another case, three different high performance disc and two different high performance gear couplings were installed before a vibration problem was traced to pipe strain induced misalignment. Other cases are presented, including some where the coupling actually was the problem. Moreover, coupling balancing is covered, especially as it relates to the overall rotor balance condition. How can you be assured that a coupling balanced at the factory will still be in balance when installed in the field? What is the importance of balancing tolerances and how significant are they when referenced to the out of balance due to fits and clearances? It is shown that the setup indication tolerances are a more significant contributor to overall coupling balance than actual balance machine unbalance tolerances. All of the cases presented involve dry couplings-ones that don't have lubricated gear teeth. On almost all new high performance turbomachinery applications, dry couplings have replaced the gear type, and one of the reasons for this is the general lack of coupling problems associated with the dry couplings (except for an occasional wind age problem). There are usually no wearing parts, and there are less clearances (like in gear tooth mesh), which can lead to significant unbalance and vibration in sensitive applications

Discovering, The Hard Way, How A High Performance Coupling Influenced The Critical Speeds And Bearing Loading Of An Overhung Radial Compressor - A Case History.

LecturePg. 67-78A case is presented where significant unacceptable vibration levels were encountered during mechanical testing of a single stage overhung radial compressor used in a mechanical vapor recompression process. The contract high performance disc coupling (modified for use between a test gearbox and the overhung compressor) was one of the main focuses of attention in arriving at a solution to the problem. Presented is the logic and courses of action taken to eliminate the coupling as the cause of the excessive vibration, and the analysis used to modify the coupling to make it the major part of the solution. This resolution involved significantly increasing the coupling's weight to change the critical speeds of the compressor rotor/bearing/coupling system, while at the same time improving the damping and stability in the coupling end bearing; enough to allow the train to run successfully. However, this extra weight coupling solution was not normal, and, except for time considerations, would not have been attempted. So, also discussed is how the actual problem (running at a critical speed without adequate damping) could have been discovered in the design stage or, once the problem occurred, been solved more easily if API procedures and guidelines had been referenced and used

Coupling Credible Failure Modes and Owner Options to Intervene

LectureWhile all machine component failures can impact reliability, cost and production, some like coupling failures may have safety risks for personnel. Intervention requires us to build appropriate steps into our machine and system designs as well as our coupling design, operation and maintenance practices. Vibration instrumentation alone can leave us vulnerable for some failure modes. In this paper, a user’s and an OEM’s views are presented of the most common coupling failure modes with examples showing details in the final stages of deterioration and identifies options to enable owners to intervene in sufficient time to prevent catastrophic failure

I Spy Transits and Pulsations: Empirical Variability in White Dwarfs Using Gaia and the Zwicky Transient Facility

We present a novel method to detect variable astrophysical objects and transient phenomena using anomalous excess scatter in repeated measurements from public catalogs of Gaia DR2 and Zwicky Transient Facility (ZTF) DR3 photometry. We first provide a generalized, all-sky proxy for variability using only Gaia DR2 photometry, calibrated to white dwarf stars. To ensure more robust candidate detection, we further employ a method combining Gaia with ZTF photometry and alerts. To demonstrate the efficacy, we apply this latter technique to a sample of roughly $12,100$ white dwarfs within 200 pc centered on the ZZ Ceti instability strip, where hydrogen-atmosphere white dwarfs are known to pulsate. Through inspecting the top $1\%$ samples ranked by these methods, we demonstrate that both the Gaia-only and ZTF-informed techniques are highly effective at identifying known and new variable white dwarfs, which we verify using follow-up, high-speed photometry. We confirm variability in all 33 out of 33 ($100\%$) observed white dwarfs within our top $1\%$ highest-ranked candidates, both inside and outside the ZZ Ceti instability strip. In addition to dozens of new pulsating white dwarfs, we also identify five white dwarfs highly likely to show transiting planetary debris; if confirmed, these systems would more than triple the number of white dwarfs known to host transiting debris.Comment: 30 pages, 14 figures, revised and accepted to ApJ on March 11, 202

High Energy Astrophysics Program (HEAP)

This report reviews activities performed by the members of the USRA contract team during the 6 months of the reporting period and projected activities during the coming 6 months. Activities take place at the Goddard Space Flight Center, within the Laboratory for High Energy Astrophysics. Developments concern instrumentation, observation, data analysis, and theoretical work in astrophysics. Supported missions include advanced Satellite for Cosmology and Astrophysics (ASCA), X-Ray Timing Experiment (XTE), X-Ray Spectrometer (XRS), Astro-E, High Energy Astrophysics Science Archive Research Center (HEASARC) and others

Investigating the genetic architecture of noncognitive skills using GWAS-by-subtraction

Little is known about the genetic architecture of traits affecting educational attainment other than cognitive ability. We used genomic structural equation modeling and prior genome-wide association studies (GWASs) of educational attainment (n = 1,131,881) and cognitive test performance (n = 257,841) to estimate SNP associations with educational attainment variation that is independent of cognitive ability. We identified 157 genome-wide-significant loci and a polygenic architecture accounting for 57% of genetic variance in educational attainment. Noncognitive genetics were enriched in the same brain tissues and cell types as cognitive performance, but showed different associations with gray-matter brain volumes. Noncognitive genetics were further distinguished by associations with personality traits, less risky behavior and increased risk for certain psychiatric disorders. For socioeconomic success and longevity, noncognitive and cognitive-performance genetics demonstrated associations of similar magnitude. By conducting a GWAS of a phenotype that was not directly measured, we offer a view of genetic architecture of noncognitive skills influencing educational success

Estimating the burden of rubella virus infection and congenital rubella syndrome through a rubella immunity assessment among pregnant women in the Democratic Republic of the Congo: Potential impact on vaccination policy.

BACKGROUND: Rubella-containing vaccines (RCV) are not yet part of the Democratic Republic of the Congo's (DRC) vaccination program; however RCV introduction is planned before 2020. Because documentation of DRC's historical burden of rubella virus infection and congenital rubella syndrome (CRS) has been minimal, estimates of the burden of rubella virus infection and of CRS would help inform the country's strategy for RCV introduction. METHODS: A rubella antibody seroprevalence assessment was conducted using serum collected during 2008-2009 from 1605 pregnant women aged 15-46years attending 7 antenatal care sites in 3 of DRC's provinces. Estimates of age- and site-specific rubella antibody seroprevalence, population, and fertility rates were used in catalytic models to estimate the incidence of CRS per 100,000 live births and the number of CRS cases born in 2013 in DRC. RESULTS: Overall 84% (95% CI 82, 86) of the women tested were estimated to be rubella antibody seropositive. The association between age and estimated antibody seroprevalence, adjusting for study site, was not significant (p=0.10). Differences in overall estimated seroprevalence by study site were observed indicating variation by geographical area (p⩽0.03 for all). Estimated seroprevalence was similar for women declaring residence in urban (84%) versus rural (83%) settings (p=0.67). In 2013 for DRC nationally, the estimated incidence of CRS was 69/100,000 live births (95% CI 0, 186), corresponding to 2886 infants (95% CI 342, 6395) born with CRS. CONCLUSIONS: In the 3 provinces, rubella virus transmission is endemic, and most viral exposure and seroconversion occurs before age 15years. However, approximately 10-20% of the women were susceptible to rubella virus infection and thus at risk for having an infant with CRS. This analysis can guide plans for introduction of RCV in DRC. Per World Health Organization recommendations, introduction of RCV should be accompanied by a campaign targeting all children 9months to 14years of age as well as vaccination of women of child bearing age through routine services

Progress report no. 1

Statement of responsibility on title-page reads: Editors: I.A. Forbes, M.J. Driscoll, D.D. Lanning, I. Kaplan, N.C. Rasmussen; Contributors: S.A. Ali, S.T. Brewer, D.K. Choi, F.M. Clikeman, W.R. Corcoran, M.J. Driscoll, I.A. Forbes, C.W. Forsberg, S.L. Ho, C.S. Kang, I. Kaplan, J.L. Klucar, D.D. Lanning, T.C. Leung, E.L. McFarland P.G. Mertens, N.R. Ortiz, A. Pant, N.A. Passman, N.C. Rasmussen, M.K. Sheaffer, D.A. Shupe, G.E. Sullivan, A.T. Supple, J.W. Synan, C.P. Tzanos, W.J. Westlake"MIT-4105-3."Includes bibliographical referencesProgress report; June 30, 1970U.S. Atomic Energy Commission contracts: AT(30-1)410