Comparison of Transient Modeling Techniques for a Micro Turbine Engine

2006 ◽  
Author(s):  
Craig R. Davison ◽  
A. M. Birk
Keyword(s):  
Gas Turbines ◽  
Relative Size ◽  
Rate Of Change ◽  
Single Stage ◽  
Radial Compression ◽  
Shaft Speed ◽  
Transient Effects ◽  
Rates Of Change ◽  
Experimental Apparatus ◽  
Transient Modeling

A large number of papers have been published on transient modeling of large industrial and military gas turbines. Few, however, have examined micro turbines. The decrease in size affects the relative rates of change of shaft speed, gas dynamics and heat soak. This paper compares the modeled transient effects of a micro turbojet engine comprised of a single stage of radial compression and a single stage of axial expansion, with a diameter of 12cm. The model was validated with experimental data. Several forms of the model were produced starting with the shaft and fuel transients. Conservation of mass, and then energy, was subsequently added for the compressor, combustor and turbine, and a large inlet plenum that was part of the experimental apparatus. Heat soak to the engine body was incorporated into both the shaft and energy models. Heat soak was considered in the compressor, combustor and turbine. Since the engine diameter appears in the differential equations to different powers, the relative rates of change vary with diameter. The rate of change of shaft speed is very strongly influenced. The responses of the different transient effects are compared. The relative solution times are also discussed, since the relative size of the required time steps changes when compared to a large engine.

scholarly journals Disease-related disability burden: a comparison of seven chronic conditions in middle-aged and older adults

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Chieh-Ying Chou ◽  
Ching-Ju Chiu ◽  
Chia-Ming Chang ◽  
Chih-Hsing Wu ◽  
Feng-Hwa Lu ◽  
...  
Keyword(s):  
Older Adults ◽  
Physical Disability ◽  
Chronic Conditions ◽  
Chronic Condition ◽  
Disease Diagnosis ◽  
Rate Of Change ◽  
Middle Aged ◽  
Rates Of Change ◽  
Depression Status ◽  
Stage Disease

Abstract Background Although previous studies have explored the effect of chronic conditions on physical disability, little is known about the levels and rates of change in physical disability after a chronic condition diagnosis in middle-aged and older adults in the Asian population. The aim of this study is to ascertain the average levels and rates of change in the development of disability after disease diagnosis, as well as to determine the influences of sociodemographic and health-related correlates in the development of disability. Methods This is a retrospective cohort study analyzing data of nationally representative participants aged 50 and over with a chronic condition or having developed one during follow-ups based on data from the 1996–2011 Taiwan Longitudinal Study on Aging (TLSA) (n = 5131). Seven chronic conditions were examined. Covariates included age at initial diagnosis, gender, education level, number of comorbidities, and depression status. Physical disability was measured by combining self-reported ADL, IADL, and strength and mobility activities with 17 total possible points, further analyzed with multilevel modeling. Results The results showed that (1) physical disability was highest for stroke, followed by cancer and diabetes at the time of the initial disease diagnosis. (2) The linear rate of change was highest for stroke, followed by lung disease and heart disease, indicating that these diseases led to higher steady increases in physical disability after the disease diagnosis. (3) The quadratic rate of change was highest in diabetes, followed by cancer and hypertension, indicating that these diseases had led to higher increments of physical disability in later stage disease. After controlling for sociodemographic and comorbidity, depression status accounted for 39.9–73.6% and 37.9–100% of the variances in the physical disability intercept and change over time, respectively. Conclusions Despite the fact that a comparison across conditions was not statistically tested, an accelerated increase in physical disabilities was found as chronic conditions progressed. While stroke and cancer lead to disability immediately, conditions such as diabetes, cancer, and hypertension give rise to higher increments of physical disability in later stage disease. Mitigating depressive symptoms may be beneficial in terms of preventing disability development in this population.

346. Measurements of the rate of change of temperature in high temperature-short time pasteurization plant

1947 ◽  
Vol 15 (1-2) ◽  
pp. 18-23
Author(s):  
F. Steghart
Keyword(s):  
High Temperature ◽  
Time Constant ◽  
Rate Of Change ◽  
Hot Water ◽  
Water Pipe ◽  
Temperature Changes ◽  
Rates Of Change ◽  
High Temperature Short Time ◽  
Short Time

It has recently been claimed that in modern high temperature-short time pasteurization plant fluctuations in temperature of the order of 1° F./sec. are unusual and probably artefacts, and that an instantaneous drop is certainly fictitious.It has, nevertheless, been shown that such rapid drops in temperature do in fact occur frequently in high temperature-short time plants of the type investigated. The plant investigated was not of the latest design incorporating devices for speeding up the control by injecting steam directly into the hot-water pipe.Temperature changes of the order of those in question were first observed by Mattick & Hiscox(1) of the National Institute for Research in Dairying, who carried out tests on pasteurization plant using a small mirror galvanometer with a very short time constant. The maximum rates of change were, however, not observed.

The Anthropocene equation

2017 ◽  
Vol 4 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Owen Gaffney ◽  
Will Steffen
Keyword(s):  
Limit Cycle ◽  
Late Quaternary ◽  
Rate Of Change ◽  
Earth System ◽  
Human Influence ◽  
Rates Of Change ◽  
The Earth ◽  
Uncertain Future ◽  
External Forces ◽  
Anthropogenic Forcings

The dominant external forces influencing the rate of change of the Earth System have been astronomical and geophysical during the planet’s 4.5-billion-year existence. In the last six decades, anthropogenic forcings have driven exceptionally rapid rates of change in the Earth System. This new regime can be represented by an ‘Anthropocene equation’, where other forcings tend to zero, and the rate of change under human influence can be estimated. Reducing the risk of leaving the glacial–interglacial limit cycle of the late Quaternary for an uncertain future will require, in the first instance, the rate of change of the Earth System to become approximately zero.

scholarly journals Environmental perturbations influence telomere dynamics in long-lived birds in their natural habitat

2013 ◽  
Vol 9 (5) ◽  
pp. 20130511 ◽  
Author(s):  
Yuichi Mizutani ◽  
Naoki Tomita ◽  
Yasuaki Niizuma ◽  
Ken Yoda
Keyword(s):  
Natural Habitat ◽  
Weather Conditions ◽  
Rate Of Change ◽  
Natural Setting ◽  
Stress Exposure ◽  
Free Living ◽  
Rates Of Change ◽  
Environmental Perturbations ◽  
Cellular Ageing ◽  
Telomere Dynamics

Telomeres are regarded as markers of biological or cellular ageing because they shorten with the degree of stress exposure. Accordingly, telomere lengths should show different rates of change when animals are faced with different intensities of environmental challenges. However, a relationship between telomere length and the environment has not yet been tested within a natural setting. Here, we report longitudinal telomere dynamics in free-living, black-tailed gulls ( Larus crassirostris ) through the recapture of birds of a known age over 2–5 consecutive years. The rate of change in telomere lengths differed with respect to year but not sex or age. The years when gulls showed stable telomere lengths or increases in telomere lengths (from 2009 to 2010) and decreases in telomere lengths (from 2010 to 2011) were characterized by El Niño and the Great Japan Earthquake, respectively. Both events are suspected to have had long-lasting effects on food availability and/or weather conditions. Thus, our findings that telomere dynamics in long-lived birds are influenced by dramatic changes in environmental conditions highlight the importance of environmental fluctuations in affecting stress and lifespan.

Thermal Influences in Gas Turbine Transients: Effects of Changes in Compressor Characteristics

1979 ◽  
Author(s):  
N. R. L. Maccallum
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Transient Response ◽  
Gas Turbines ◽  
Axial Flow ◽  
Transient Heat Transfer ◽  
Shaft Speed ◽  
Delivery Pressure ◽  
Surge Line ◽  
Transfer Parameters

During transients of axial-flow gas turbines, the characteristics of the compressor are altered. The changes in these characteristics (excluding surge line changes) have been related to transient heat transfer parameters, and these relations have been incorporated in a program for predicting the transient response of a single-shaft aero gas turbine. The effect of the change in compressor characteristics has been examined in accelerations using two alternative acceleration fuel schedules. When the fuel is scheduled on compressor delivery pressure alone. there is no increase in predicted acceleration times. When the fuel is scheduled on shaft speed alone, the predicted acceleration times are increased by about 5 to 6 percent.

An Advanced Single-Stage Turbine Facility for Investigating Non-Axisymmetric Contoured Endwalls in the Presence of Purge Flow

2019 ◽  
Author(s):  
Robin R. Jones ◽  
Oliver J. Pountney ◽  
Bjorn L. Cleton ◽  
Liam E. Wood ◽  
B. Deneys J. Schreiner ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Static Pressure ◽  
Optical Measurement ◽  
Guide Vane ◽  
Single Stage ◽  
Test Facility ◽  
Pressure Distributions ◽  
Mainstream Flow ◽  
Purge Flow ◽  
Nozzle Guide

Abstract In modern gas turbines, endwall contouring (EWC) is employed to modify the static pressure field downstream of the vanes and minimise the growth of secondary flow structures developed in the blade passage. Purge flow (or egress) from the upstream rim-seal interferes with the mainstream flow, adding to the loss generated in the rotor. Despite this, EWC is typically designed without consideration of mainstream-egress interactions. The performance gains offered by EWC can be reduced, or in the limit eliminated, when purge air is considered. In addition, EWC can result in a reduction in sealing effectiveness across the rim seal. Consequently, industry is pursuing a combined design approach that encompasses the rim-seal, seal-clearance profile and EWC on the rotor endwall. This paper presents the design of, and preliminary results from a new single-stage axial turbine facility developed to investigate the fundamental fluid dynamics of egress-mainstream flow interactions. To the authors’ knowledge this is the only test facility in the world capable of investigating the interaction effects between cavity flows, rim seals and EWC. The design of optical measurement capabilities for future studies, employing volumetric velocimetry and planar laser induced fluorescence are also presented. The fluid-dynamically scaled rig operates at benign pressures and temperatures suited to these techniques and is modular. The facility enables expedient interchange of EWC (integrated into the rotor bling), blade-fillet and rim-seals geometries. The measurements presented in this paper include: gas concentration effectiveness and swirl measurements on the stator wall and in the wheel-space core; pressure distributions around the nozzle guide vanes at three different spanwise locations; pitchwise static pressure distributions downstream of the nozzle guide vane at four axial locations on the stator platform.

scholarly journals On the Regularity of Fluctuations in Annual and Secular Polar Motions

1972 ◽  
Vol 48 ◽  
pp. 61-67
Author(s):  
H. J. Abraham
Keyword(s):  
Rate Of Change ◽  
Rates Of Change ◽  
Amplitude Fluctuations ◽  
Chandler Frequency ◽  
Do So

It may become possible to explain much of the behaviour and remarkable regularity of fluctuations in reported annual and secular polar motions if the potential that causes an immediate excitation is also a factor in that excitation's rate of change afterwards.The Chandler frequency, for example, being a function of the deformation excitation, should then vary with the librational and nutational displacements of the pole of rotation. It is found that the frequency does in fact do so.The annual excitation would be affected as well. The steady and seasonal primary excitations are known to cause free and forced nutations that are accompanied by periodic secondary excitations. These would arise partly at once and partly in the course of time; they would modulate the primary annual excitation and also one another, according to the period of the beats between the annual and Chandler nutations. It is found that the reported annual excitation shows phase and amplitude fluctuations of this kind. (The data also show another large excitation that occurred briefly on two occasions).Finally, the amplitude and phase of the secular librations appear to have followed an expression that is obtained by integrating the rates of change of excitation. This expression is a function of the amplitude of the annual excitation and the period of the beats between the annual and Chandler nutations.

scholarly journals Period Changes in Magellanic Cloud Cepheids

1984 ◽  
Vol 108 ◽  
pp. 227-228
Author(s):  
H. Deasy ◽  
P. A. Wayman
Keyword(s):  
South African ◽  
Variable Stars ◽  
Period Change ◽  
Magellanic Clouds ◽  
Rate Of Change ◽  
Data Sets ◽  
Fractional Change ◽  
Rates Of Change ◽  
Observatory Data ◽  
Irregular Period

It has been found possible to obtain information on period change in data on 115 cepheid variable stars in the Magellanic Clouds (84 LMC cepheids and 31 SMC cepheids). Harvard Observatory data of the period 1910 to 1950 (collated by Payne-Gaposchkin and Gaposchkin) are combined with Dunsink Observatory observations carried out by C.J. Butler in 1966/67 and with South African Astronomical Observatory observations covering the years 1975–1977 by Martin, Thomas, Carter and Davies to derive mean periods for the intervals between the various data sets. Using these new periods in conjunction with the very accurate Harvard periods, seperate estimates of the time averaged fractional change of period per day, d/dt (ln P), with corresponding estimated errors, could be evaluated for two epochs, one around 1950 and the other around 1971. It was found that 70 stars give rates of change of period that are not significantly different from zero, that 20 stars have two values of rate of change of period that are in agreement at the two epochs (indicative of secular period change), while 22 stars give two disparate values of rate of change of period (indicative of irregular period changes).

Monetary Trends in the United States and the United Kingdom, 1878–1970: Selected Findings

1975 ◽  
Vol 35 (1) ◽  
pp. 138-159 ◽  
Author(s):  
Anna Jacobson Schwartz
Keyword(s):  
United States ◽  
United Kingdom ◽  
Interest Rates ◽  
The United States ◽  
Rate Of Change ◽  
Final Phase ◽  
Expansion Phase ◽  
Rates Of Change ◽  
The United Kingdom ◽  
Successive Phase

Milton Friedman and I have been engaged for some time in a study of the characteristic behavior of the quantity of money over long periods in relation to income, prices, and interest rates m the United States and the United Kingdom. In our study, our observations of levels are the average annual values of each variable during cyclical phases, starting with the expansion phase of 1878–1882 in the United States and 1879–1883 in the United Kingdom, and ending with the final phase that can be marked off for each country, respectively, 1969–1970 and 1968–1969. In all, we have forty-five observations of levels for the United States, and thirtythree for the United Kingdom. In addition to levels of observation, we also examine rates of change, which we express as the slopes of least-squares lines connecting three successive phase averages. For each country, the rate-of-change observations are two fewer than the number of level observations.

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