bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of inositol 1,4,5‐trisphosphate receptors in Ca2+ signalling and the generation of arrhythmias in rat atrial myocytes
Authors: Mackenzie Lauren , Bootman Martin D. , Laine Mika , Berridge Michael J. , Jan Thuring  , Holmes Andrew , Li Wen‐Hong , Lipp Peter
Published: July 2002

Various cardio‐active stimuli, including endothelin‐1 (ET‐1), exhibit potent arrhythmogenicity, but the underlying cellular mechanisms of their actions are largely unclear. We used isolated rat atrial myocytes and related changes in their subcellular Ca2+ signalling to the ability of various stimuli to induce diastolic, premature extra Ca2+ transients (ECTs). For this, we recorded global and spatially resolved Ca2+ signals in indo‐1‐ and fluo‐4‐loaded atrial myocytes during electrical pacing. ET‐1 exhibited a higher arrhythmogenicity (arrhythmogenic index; ratio of number of ECTs over fold‐increase in Ca2+ response, 8.60; n= 8 cells) when compared with concentrations of cardiac glycosides (arrhythmogenic index, 4.10; n= 8 cells) or the β‐adrenergic agonist isoproterenol (arrhythmogenic index, 0.11; n= 6 cells) that gave similar increases in the global Ca2+ responses. Seventy‐five percent of the ET‐1‐induced arrhythmogenic Ca2+ transients were accompanied by premature action potentials, while for digoxin this proportion was 25 %. The β‐adrenergic agonist failed to elicit a significant number of ECTs. Direct activation of inositol 1,4,5‐trisphosphate (InsP3) receptors with a membrane‐permeable InsP3 ester (InsP3 BM) mimicked the effect of ET‐1 (arrhythmogenic index, 14.70; n= 6 cells). Inhibition of InsP3 receptors using 2 μM 2‐aminoethoxydiphenyl borate, which did not display any effects on Ca2+ signalling under control conditions, specifically suppressed the arrhythmogenic action of ET‐1 and InsP3 BM. Immunocytochemistry indicated a co‐localisation of peripheral, junctional ryanodine receptors with InsP3Rs. Thus, the pronounced arrhythmogenic potency of ET‐1 is due to the spatially specific recruitment of Ca2+ sparks by subsarcolemmal InsP3Rs. Summation of such sparks efficiently generates delayed afterdepolarisations that trigger premature action potentials. We conclude that the particular spatial profile of cellular Ca2+ signals is a major, previously unrecognised, determinant for arrhythmogenic potency and that the InsP3 signalling cassette might therefore be a promising new target for understanding and managing atrial arrhythmia.
Molecular aspects of acute inhibition of Na+‐H+ exchanger NHE3 by A2‐adenosine receptor agonists
Authors: Di Sole Francesca , Cerull Robert , Casavola Valeria , Moe Orson W. , Burckhardt Gerhard , Helmle‐Kolb Corinna
Published: July 2002

Adenosine regulates Na+ homeostasis by its acute effects on renal Na+ transport. We have shown in heterologously transfected A6/C1 cells (renal cell line from Xenopus laevis) that adenosine‐induced natriuresis may be effected partly via A2 adenosine receptor‐mediated inactivation of the renal brush border membrane Na+‐H+ exchanger NHE3. In this study we utilized A6/C1 cells stably expressing wild‐type as well as mutated forms of NHE3 to assess the molecular mechanism underlying A2‐dependent control of NHE3 function. Cell surface biotinylation combined with immunoprecipitation revealed that NHE3 is targeted exclusively to the apical domain and that the endogenous Xenopus NHE is located entirely on the basolateral side of A6/C1 transfectants. Stimulation of A2‐adenosine receptors located on the basolateral side for 15 min with CPA (N6‐cyclopentyladenosine) acutely decreased NHE3 activity (microspectrofluorimety). This effect was mimicked by 8‐bromo‐cAMP and entirely blocked by pharmacological inhibition of PKA (with H89) or singular substitution of two PKA target sites (serine 552 and serine 605) on NHE3. Downregulation of NHE3 activity by CPA was attributable to a reduction of NHE3 intrinsic transport activity without change in surface NHE3 protein at 15 min. At 30 min, the decrease in transport activity was associated with a decrease in apical membrane NHE3 antigen. In conclusion, two highly conserved target serine sites on NHE3 determine NHE3 modulation upon A2‐receptor activation and NHE3 inactivation by adenosine proceeds via two phases with distinct mechanisms.
Role of anion‐cation interactions on the pre‐steady‐state currents of the rat Na+‐Cl−‐dependent GABA cotransporter rGAT1
Authors: Bossi Elena , Giovannardi Stefano , Binda Francesca , Forlani Greta , Peres Antonio
Published: July 2002

The effects of sodium and chloride on the properties of the sodium‐dependent component of the ‘pre‐steady‐state’ currents of rGAT1, a GABA cotransporter of the Na+‐Cl−‐dependent family, were studied using heterologous oocyte expression and voltage clamp. Reductions in either extracellular sodium or chloride shifted the charge‐voltage (Q‐V) and time constant‐voltage (τ‐V) characteristics of the process towards more negative potentials. The shift induced by sodium (TMA+, tetramethylammonium substitution) was stronger than that induced by chloride (acetate substitution), and the shift of τ was accompanied by a decrease in its maximum value. Increasing extracellular Ca2+ did not produce significant shifts in Q‐V and τ‐V curves. The negative shift of the Q‐V curve upon chloride reduction and the decrease in the value of the relaxation time constant, τ, when either sodium or chloride were lowered, contrasted with the prediction of the Hill‐Boltzmann interpretation of the process. Analysis of the unidirectional rate constants under different conditions revealed that both sodium and chloride shifted the outward rate more than the inward rate; furthermore, the shifts induced by sodium were larger than those induced by chloride. These observations are qualitatively compatible with the existence of a selective vestibule at the mouth of the transporters, acting similarly to a Donnan system.
Vesicle pool partitioning influences presynaptic diversity and weighting in rat hippocampal synapses
Authors: Waters Jack , Smith Stephen J
Published: July 2002

Hippocampal synapses display a range of release probabilities. This is partially the result of scaling of release probability with the total number of releasable vesicles at each synapse. We have compared synaptic release and vesicle pool sizes across a large number of hippocampal synapses using FM 1‐43 and confocal fluorescence microscopy. We found that the relationship between the number of recycling vesicles at a synapse and its release probability is dependent on firing frequency. During firing at 10 Hz, the release probability of each synapse is closely related to the number of recycling vesicles that it contains. In contrast, during firing at 1 Hz, different synapses turn over their recycling vesicle pools at different rates leading to an indirect relationship between recycling vesicle pool size and release probability. Hence two synapses may release vesicles at markedly different rates during low frequency firing, even if they contain similar numbers of vesicles. Both further kinetic analyses and manipulation of the number of vesicles in the readily releasable pool using phorbol ester treatment suggested that this imprecise scaling observed during firing at 1 Hz resulted from synapse‐to‐synapse differences in the proportion of recycling vesicles partitioned into the readily releasable pool. Hence differential partitioning between vesicle pools affects presynaptic weighting in a frequency‐dependent manner. Since hippocampal single unit firing rates shift between 1 Hz and 10 Hz regimes with behavioural state, differential partitioning may be a mechanism for encoding information in hippocampal circuits.
Role of intracellular and extracellular pH in the chemosensitive response of rat locus coeruleus neurones
Authors: Filosa J. A. , Dean J. B. , Putnam R. W.
Published: July 2002

The chemosensitive response of locus coeruleus (LC) neurones to changes in intracellular pH (pHi), extracellular pH (pHo) and molecular CO2 were investigated using neonatal rat brainstem slices. A new technique was developed that involves the use of perforated patch recordings in combination with fluorescence imaging microscopy to simultaneously measure pHi and membrane potential (Vm). Hypercapnic acidosis (15 % CO2, pHo 6.8) resulted in a maintained fall in pHi of 0.31 pH units and a 93 % increase in the firing rate of LC neurones. On the other hand, isohydric hypercapnia (15 % CO2, 77 mm HCO3−, pHo 7.45) resulted in a smaller and transient fall in pHi of about 0.17 pH units and an increase in firing rate of 76 %. Acidified Hepes (N‐2‐hydroxyethylpiperazine‐N′‐2‐ ethanesulfonic acid)‐buffered medium (pHo 6.8) resulted in a progressive fall in pHi of over 0.43 pH units and an increase in firing rate of 126 %. Isosmotic addition of 50 mm propionate to the standard HCO3−‐buffered medium (5 % CO2, 26 mm HCO3−, pHo 7.45) resulted in a transient fall in pHi of 0.18 pH units but little increase in firing rate. Isocapnic acidosis (5 % CO2, 7 mm HCO3−, pHo 6.8) resulted in a slow intracellular acidification to a maximum fall of about 0.26 pH units and a 72 % increase in firing rate. For all treatments, the changes in pHi preceded or occurred simultaneously with the changes in firing rate and were considerably slower than the changes in pHo. In conclusion, an increased firing rate of LC neurones in response to acid challenges was best correlated with the magnitude and the rate of fall in pHi, indicating that a decrease in pHi is a major part of the intracellular signalling pathway that transduces an acid challenge into an increased firing rate in LC neurones.
Cardiac titin: an adjustable multi‐functional spring
Authors: Granzier Henk , Labeit Siegfried
Published: July 2002

The giant elastic protein titin contains a molecular spring segment that underlies the majority of myocardial passive stiffness. The mechanical characteristics of this spring may be tuned to match changing mechanical demands placed on muscle, using mechanisms that operate on different time scales and that include post‐transcriptional and post‐translational processes. Recent work also suggests that titin performs roles that go beyond passive stiffness generation. In contracting myocardium, titin may modulate actomyosin interaction by a titin‐based alteration of the distance between myosin heads and actin. Furthermore, novel ligands have been identified that link titin to membrane channels, protein turnover and gene expression. This review highlights that titin is a versatile and adjustable spring with a range of important functions in passive and contracting myocardium.
Role of 5′AMP‐activated protein kinase in glycogen synthase activity and glucose utilization: insights from patients with McArdle's disease
Authors: Nielsen Jakob N. , Wojtaszewski Jørgen F. P. , Haller Ronald G. , Hardie D. Grahame , Kemp Bruce E. , Richter Erik A. , Vissing John
Published: July 2002

It has been suggested that 5′AMP‐activated protein kinase (AMPK) is involved in the regulation of glucose and glycogen metabolism in skeletal muscle. We used patients with chronic high muscle glycogen stores and deficient glycogenolysis (McArdle's disease) as a model to address this issue. Six McArdle patients were compared with control subjects during exercise. Muscle α2AMPK activity increased in McArdle patients (from 1.3 ± 0.2 to 1.9 ± 0.2 pmol min−1 mg−1, P= 0.05) but not in control subjects (from 1.0 ± 0.1 to 1.3 ± 0.3 pmol min−1 mg−1). Exercise‐induced phosphorylation of the in vivo AMPK substrate acetyl CoA carboxylase (ACCβ; Ser221) was higher (P < 0.01) in McArdle patients than in control subjects (18 ± 3 vs. 10 ± 1 arbitrary units). Exercise‐induced whole‐body glucose utilization was also higher in McArdle patients than in control subjects (P < 0.05). No correlation between individual AMPK or ACCβ values and glucose utilization was observed. Glycogen synthase (GS) activity was decreased in McArdle patients from 11 ± 1.3 to 5 ± 1.2 % (P < 0.05) and increased in control subjects from 19 ± 1.6 to 23 ± 2.3 % (P < 0.05) in response to exercise. This was not associated with activity changes of GS kinase 3 or protein phosphatase 1, but the changes in GS activity could be due to changes in activity of AMPK or protein kinase A (PKA) as a negative correlation between either ACCβ phosphorylation (Ser221) or plasma adrenaline and GS activity was observed. These findings suggest that GS activity is increased by glycogen breakdown and decreased by AMPK and possibly PKA activation and that the resultant GS activity depends on the relative strengths of the various stimuli. Furthermore, AMPK may be involved in the regulation of glucose utilization during exercise in humans, although the lack of correlation between individual AMPK activity or ACCβ phosphorylation (Ser221) values and individual glucose utilization during exercise implies that AMPK may not be an essential regulator.
Effect of exogenous and endogenous angiotensin II on intrarenal distribution of glomerular filtration rate in rats
Authors: Treeck Birte , Beatrice Roald Anca , Tenstad Olav , Aukland Knut
Published: July 2002

Different changes in glomerular filtration rates (GFR) in deep and superficial glomeruli have been suggested to influence renal NaCl excretion and concentrating ability. Angiotensin II (AngII) has been implicated in such changes, but the experimental evidence has been conflicting, probably because of the methodological limitation of just one ‘snapshot’ measurement of local GFR per kidney. We have therefore studied the effect of AngII and AT1‐receptor blockade on glomerular filtration in outer, middle and inner cortex (OC, MC and IC, respectively) in pentobarbitone‐anaesthetised rats using the aprotinin (Ap) method, providing control and experimental measurements in the same kidney. Glomerular filtration rate per gram cortical tissue was measured based on ‘free’ glomerular filtration of Ap followed by complete tubular uptake and a 20 min sojourn in the proximal tubular cells before breakdown and incipient return to the plasma.125I‐labelled Ap was injected i.v. to determine control Ap clearance, followed after 13 min by injection of AngII or the A1 type AngII receptor blocker losartan and 2 min thereafter by 131I‐labelled Ap to determine clearance in the experimental period. Tracer activity in frequent blood samples and in tissue samples allowed calculation of GFR in the two periods. Mean GFR control values were: 1.13 ml min−1 in whole kidney and 1.44, 1.27 and 0.76 ml min−1 per gram cortical tissue in OC, MC and IC, respectively. The most sensitive and comprehensive measure of altered GFR distribution is the ratio between the relative filtration change in inner versus that in outer cortex, F= (ICE/ICC)/(OCE/OCC), where subscripts E and C stand for experimental and control, respectively. F values greater than 1.00 directly indicate and quantify a relatively greater increase of filtration rate in inner than in outer cortex. We found in salt‐replete rats that at practically unchanged total GFR, intravenous and intra‐arterial infusion of AngII increased F to 1.07 and 1.04 (P < 0.05) whereas losartan reduced F to 0.99. After pretreatment with the inhibitor of nitric oxide production L‐NAME, losartan increased total GFR by 8 % and F fell to 0.95 (P < 0.05). In salt‐depleted rats losartan reduced F to 0.95 (P < 0.05) at unchanged total GFR. All IC/OC changes induced by losartan were significantly different from that obtained by AngII infusions. We conclude that deep nephrons have higher postglomerular AngII tone and also higher AngII sensitivity than superficial nephrons. The better preserved GFR in deep cortex during AngII action may contribute towards maintaining the renal concentrating ability by providing NaCl for reabsorption by the ascending limb of the loop of Henle.
Aquaporin water channels – from atomic structure to clinical medicine
Authors: Agre Peter , King Landon S. , Yasui Masato , Guggino Wm B. , Ottersen Ole Petter , Fujiyoshi Yoshinori , Engel Andreas , Nielsen Søren
Published: July 2002

The water permeability of biological membranes has been a longstanding problem in physiology, but the proteins responsible for this remained unknown until discovery of the aquaporin 1 (AQP1) water channel protein. AQP1 is selectively permeated by water driven by osmotic gradients. The atomic structure of human AQP1 has recently been defined. Each subunit of the tetramer contains an individual aqueous pore that permits single‐file passage of water molecules but interrupts the hydrogen bonding needed for passage of protons. At least 10 mammalian aquaporins have been identified, and these are selectively permeated by water (aquaporins) or water plus glycerol (aquaglyceroporins). The sites of expression coincide closely with the clinical phenotypes ‐ ranging from congenital cataracts to nephrogenic diabetes insipidus. More than 200 members of the aquaporin family have been found in plants, microbials, invertebrates and vertebrates, and their importance to the physiology of these organisms is being uncovered.
Reaction Mechanisms for Methane Ignition
Authors: Li S. C. , Williams F. A.
Published: July 2002

To help understand how methane ignition occurs in gas turbines, dual-fuel diesel engines, and other combustion devices, the present study addresses reaction mechanisms with the objective of predicting autoignition times for temperatures between 1000 K and 2000 K, pressures between 1 bar and 150 bar, and equivalence ratio between 0.4 and 3. It extends our previous methane flame chemistry and refines earlier methane ignition work. In addition to a detailed mechanism, short mechanisms are presented that retain essential features of the detailed mechanism. The detailed mechanism consists of 127 elementary reactions among 31 species and results in nine intermediate species being most important in autoignition, namely, CH3, OH, HO2,H2O2,CH2O,CHO, CH3O, H, O. Below 1300 K the last three of these are unimportant, but above 1400 K all are significant. To further simplify the computation, systematically reduced chemistry is developed, and an analytical solution for ignition delay times is obtained in the low-temperature range. For most fuels, a single Arrhenius fit for the ignition delay is adequate, but for hydrogen the temperature sensitivity becomes stronger at low temperatures. The present study predicts that, contrary to hydrogen, for methane the temperature sensitivity of the autoignition delay becomes stronger at high temperatures, above 1400 K, and weaker at low temperatures, below 1300 K. Predictions are in good agreement with shock-tube experiments. The results may be employed to estimate ignition delay times in practical combustors.
Use of Detailed Chemical Kinetics to Study HCCI Engine Combustion With Consideration of Turbulent Mixing Effects
Authors: Kong S.-C. , Reitz R. D.
Published: July 2002

Detailed chemical kinetics was used in an engine CFD code to study the combustion process in HCCI engines. The CHEMKIN code was implemented in KIVA such that the chemistry and flow solutions were coupled. The reaction mechanism consists of hundreds of reactions and species and is derived from fundamental flame chemistry. Effects of turbulent mixing on the reaction rates were also considered. The results show that the present KIVA/CHEMKIN model is able to simulate the ignition and combustion process in three different HCCI engines including a CFR engine and two modified heavy-duty diesel engines. Ignition timings were predicted correctly over a wide range of engine conditions without the need to adjust any kinetic constants. However, it was found that the use of chemical kinetics alone was not sufficient to accurately simulate the overall combustion rate. The effects of turbulent mixing on the reaction rates need to be considered to correctly simulate the combustion and heat release rates.
The μ Approach to Control of Active Magnetic Bearings
Authors: Fittro R. L. , Knospe C. R.
Published: July 2002

Many important industrial problems in the control of rotating machinery with active magnetic bearings concern the minimization of the rotor vibration response to poorly characterized disturbances at a single or several shaft locations, these typically not corresponding to those of a sensor or actuator. Herein, we examine experimental results of a multivariable controller obtained via μ synthesis with a laboratory test rig. These indicate that a significant improvement in performance can be obtained with a multivariable μ controller over that achieved with an optimal decentralized PD controller.
Application of an Internally Consistent Material Model to Determine the Effect of Tool Edge Geometry in Orthogonal Machining
Authors: Schimmel Roy J. , Endres William J. , Stevenson Robin
Published: July 2002

It is well known that the edge geometry of a cutting tool affects the forces measured in metal cutting. Two experimental methods have been suggested in the past to extract the ploughing (noncutting) component from the total measured force: (1) the extrapolation approach and (2) the dwell force technique. This study reports the behavior of zinc during orthogonal machining using tools of controlled edge radius. Application of both the extrapolation and dwell approaches showed that neither produces an analysis that yields a material response consistent with the known behavior of zinc. Further analysis shows that the edge geometry modifies the shear zone of the material and thereby modifies the forces. When analyzed this way, the measured force data yield the expected material response without requiring recourse to an additional ploughing component.
Pressure Surface Separations in Low-Pressure Turbines—Part 1: Midspan Behavior
Authors: Brear Michael J. , Hodson Howard P. , Harvey Neil W.
Published: July 2002

This paper describes an investigation into the behavior of the pressure surface separation at midspan in a linear cascade. It is found that the pressure surface separation can be a significant contributor to the profile loss of a thin, solid, low-pressure turbine blade that is typical of current engine designs. Numerical predictions are first used to study the inviscid behavior of the blade. These show a strong incidence dependence around the leading edge of the profile. Experiments then show clearly that all characteristics of the pressure surface separation are controlled primarily by the incidence. It is also shown that the effects of wake passing, freestream turbulence and Reynolds number are of secondary importance. A simple two-part model of the pressure surface flow is then proposed. This model suggests that the pressure surface separation is highly dissipative through the action of its strong turbulent shear. As the incidence is reduced, the increasing blockage of the pressure surface separation then raises the velocity in the separated shear layer to levels at which the separation can create significant loss.
A New Method for Dynamic Analysis of Mistuned Bladed Disks Based on the Exact Relationship Between Tuned and Mistuned Systems
Authors: Petrov E. P. , Sanliturk K. Y. , Ewins D. J.
Published: July 2002

A new method for the dynamic analysis of mistuned bladed disks is presented. The method is based on exact calculation of the response of a mistuned system using response levels for the tuned assembly together with a modification matrix constructed from the frequency response function (FRF) matrix of the tuned system and a matrix describing the mistuning. The main advantages of the method are its efficiency and accuracy, which allow the use of large finite element models of practical bladed disk assemblies in parametric studies of mistuning effects on vibration amplitudes. A new method of calculating the FRF matrix of the tuned system using a sector model is also developed so as to improve the efficiency of the method even further, making the proposed method a very attractive tool for mistuning studies. Various numerical aspects of the proposed method are addressed and its accuracy and efficiency are demonstrated using representative test cases.
Analysis of the Effects of Water Injection on the Performance of a Gas Turbine
Authors: Mathioudakis K.
Published: July 2002

The effect of water injection in the combustion chamber of an industrial gas turbine is studied by means of analytic relations. Equations for the estimation of changes in the main performance parameters are provided. The relations are derived on the basis of an order of magnitude analysis and taking into account variation of gas properties due to water injection as well as changes in the interrelation of component performance parameters. It is shown that water/fuel ratio is the main parameter on which performance deviations depend. Data from the performance testing of an industrial gas turbine are used to check the validity of the proposed relations. The comparison of the predictions to the test data shows that the mechanisms of performance deviations are well modeled by the analysis presented.
On Application of Nonlinear k-ε Models for Internal Combustion Engine Flows
Authors: Bianchi G. M. , Cantore G. , Parmeggiani P. , Michelassi V.
Published: July 2002

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.
Boundary Layer Development in the BR710 and BR715 LP Turbines—The Implementation of High-Lift and Ultra-High-Lift Concepts
Authors: Howell R. J. , Hodson H. P. , Schulte V. , Stieger R. D. , Schiffer Heinz-Peter , Haselbach F. , Harvey N. W.
Published: July 2002

This paper describes a detailed study into the unsteady boundary layer behavior in two high-lift and one ultra-high-lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high-lift and ultra-high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles. Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high-lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two-stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high-lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra-high-lift profile represents a 12 percent reduction in blade numbers compared to the original BR715 turbine. The results from NGV2 on all of the turbines show “classical” unsteady boundary layer behavior. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.
Condensation Heat Transfer on Enhanced Surface Tubes: Experimental Results and Predictive Theory
Authors: Belghazi M. , Bontemps A. , Marvillet C.
Published: July 2002

Condensation heat transfer in a bundle of horizontal enhanced surface copper tubes (Gewa C+ tubes) has been experimentally investigated, and a comparison with trapezoidal shaped fin tubes with several fin spacing has been made. These tubes have a specific surface three-dimensional geometry (notched fins) and the fluids used are either pure refrigerant (HFC134a) or binary mixtures of refrigerants (HFC23/HFC134a). For the pure fluid and a Gewa C+ single tube, the results were analyzed with a specifically developed model, taking into account both gravity and surface tension effects. For the bundle and for a pure fluid, the inundation of the lowest tubes has a strong effect on the Gewa C+ tube performances contrary to the finned tubes. For the mixture, the heat transfer coefficient decreases dramatically for the Gewa C+ tube.
Aerodynamic Design and Testing of an Axial Flow Compressor With Pressure Ratio of 23.3:1 for the LM2500+ Gas Turbine
Authors: Wadia A. R. , Wolf D. P. , Haaser F. G.
Published: July 2002

The LM2500+ gas turbine, rated between 39,000–40,200 shaft horsepower (shp), was introduced for field service in 1998. This growth aero-derivative gas turbine is suitable for a variety of power generation applications, such as co-generation and combined cycle, as well as mechanical drive applications. At the heart of the LM2500+ 25% power increase is an up-rated derivative 17-stage axial compressor. This paper describes the aerodynamic design and development of this high-pressure ratio single-spool compressor for the LM2500+ gas turbine. The compressor is derived by zero-staging the highly efficient and reliable LM2500 compressor to increase the flow by 23% at a pressure ratio of 23.3:1. The aerodynamic efficiency of the compressor is further improved by using three-dimensional, custom-tailored airfoil designs similar to those used in the CF6-80C2 high-pressure compressor. The compressor achieved a peak polytropic efficiency above 91%, meeting all its operability objectives. The technical requirements and overall aerodynamic design features of the compressor are presented first. Next, the zero stage match point selection is described and the procedure used to set up the vector diagrams using a through-flow code with secondary flow and mixing is outlined. Detailed design results for the new transonic airfoils in the compressor using three-dimensional viscous analysis are presented. The compressor instrumentation and performance test results are discussed. The performance of the zero stage is separated from that of the baseline compressor with the CF6-80C2 airfoils to show the improvement in efficiency with the new airfoils.
Displacement Boundary Value Problem of Piezoelectric Material Plane With an Elliptic Hole
Authors: Hao T.-H.
Published: July 2002

In this paper, the displacement boundary value problem of a piezoelectric material plane with an elliptic hole is studied. As the permittivity of the medium in the hole is far less than that of the piezoelectric material, the electric induction of the medium is negligible. An exact solution is obtained. Its application to the inclusion problem has been given. The components of the stress tensor are discussed.
Isoparametric Graded Finite Elements for Nonhomogeneous Isotropic and Orthotropic Materials
Authors: Kim Jeong-Ho , Paulino G. H.
Published: July 2002

Graded finite elements are presented within the framework of a generalized isoparametric formulation. Such elements possess a spatially varying material property field, e.g. Young’s modulus E and Poisson’s ratio ν for isotropic materials; and principal Young’s moduli E11,E22, in-plane shear modulus G12, and Poisson’s ratio ν12 for orthotropic materials. To investigate the influence of material property variation, both exponentially and linearly graded materials are considered and compared. Several boundary value problems involving continuously nonhomogeneous isotropic and orthotropic materials are solved, and the performance of graded elements is compared to that of conventional homogeneous elements with reference to analytical solutions. Such solutions are obtained for an orthotropic plate of infinite length and finite width subjected to various loading conditions. The corresponding solutions for an isotropic plate are obtained from those for the orthotropic plate. In general, graded finite elements provide more accurate local stress than conventional homogeneous elements, however, such may not be the case for four-node quadrilateral (Q4) elements. The framework described here can serve as the basis for further investigations such as thermal and dynamic problems in functionally graded materials.
A Mechanism of Low Subharmonic Response in Rotor/Stator Contact—Measurements and Simulations
Authors: von Groll Go¨tz , Ewins David J.
Published: July 2002

There are a variety of abnormal running conditions in rotating machinery that lead to rotor/stator interaction dynamics which, in turn, have a range of effects associated with them. One of these effects is steady vibration response at frequencies which are different from the excitation. This paper describes a mechanism of generating subharmonic vibration frequencies in both numerical simulation and measurements, which are obtained from a study of the relatively new problem of “windmilling imbalance” in aero-engines. What is different from other nonlinear systems with, say, clearance or squeeze film dampers, is the richness of the frequency spectrum.
Vibration Analysis of Rotors Utilizing Implicit Directional Information of Complex Variable Descriptions
Authors: Kessler C. , Kim J.
Published: July 2002

A complex variable description of planar motion incorporates directivity as inherent information which is therefore very convenient in vibration analysis of rotors. This paper proposes to use the directional information explicitly when the equation of motion of a rotor is formulated in complex variables. It is shown that the free vibration solution to the equation of motion formulated as such can be defined as the directional natural mode because it describes not only the shape and frequency but also the direction of the free vibration response. The directional frequency response functions (dFRFs) that have been used recently are obtained as the solution to the forced vibration solution to the equation of motion. Symmetric and anti-symmetric motions of a geometrically symmetric rigid rotor are used as examples to explain these concepts and their practical significances. The proposed approach allows clear understanding and definitions of some unique characteristics of rotor vibrations, such as the forward and backward modes, and forward and backward critical speeds, which have been often used in confusing or incorrect ways.
Dynamic Simulation of Full Startup Procedure of Heavy-Duty Gas Turbines
Authors: Kim J. H. , Song T. W. , Kim T. S. , Ro S. T.
Published: July 2002

A simulation program for transient analysis of the startup procedure of heavy duty gas turbines for power generation has been constructed. Unsteady one-dimensional conservation equations are employed and equation sets are solved numerically using a fully implicit method. A modified stage-stacking method has been adopted to estimate the operation of the compressor. Compressor stages are grouped into three categories (front, middle, rear), to which three different stage characteristic curves are applied in order to consider the different low-speed operating characteristics. Representative startup sequences were adopted. The dynamic behavior of a representative heavy duty gas turbine was simulated for a full startup procedure from zero to full speed. Simulated results matched the field data and confirmed unique characteristics such as the self-sustaining and the possibility of rear-stage choking at low speeds. Effects of the estimated schedules on the startup characteristics were also investigated. Special attention was paid to the effects of modulating the variable inlet guide vane on startup characteristics, which play a key role in the stable operation of gas turbines.
Ride Dynamics of Nonlinear Vehicle Models Using Component Mode Synthesis
Authors: Verros G. , Natsiavas S.
Published: July 2002

A general methodology is presented for investigating ride dynamics of large order vehicle models in a systematic and computationally efficient way. First, the equations of motion of representative vehicle models are set up by applying classical finite element techniques. In the simplest version of these models, the important system parameters are assumed to be constant, leading to linear formulations. Then, more accurate and involved models are examined by including typical nonlinearities in the tires and the shock absorbers of the vehicle suspension. Also, emphasis is placed on taking into account the possibility of temporary separation of a wheel from the ground. These models are strongly nonlinear and as their order increases the existing numerical methodologies for a systematic determination of their dynamics become inefficient to apply. Therefore, the first step of the present methodology is to reduce the dimensions of the original system by applying a component mode synthesis approach. Subsequently, this allows the application of appropriate numerical methodologies for predicting response spectra of the nonlinear models to periodic road excitations. Finally, results obtained by direct integration of the equations of motion are also presented for transient road excitation. In all cases, the accuracy and validity of the applied methodology is verified by comparison with results obtained for the original models.
Structural Acoustic Optimization of a Composite Cylindrical Shell Using FEM/BEM
Authors: Johnson W. M. , Cunefare K. A.
Published: July 2002

A finite element/boundary element design tool is used to perform a structural acoustic optimization on an eight-ply graphite epoxy cylindrical shell. The shell is subject to two external monopole sources vibrating at a single frequency. The goal of the optimization is the minimization of the sum of the squared pressure amplitudes within the enclosed acoustic cavity. The ply angles serve as the design variables in optimization. The optimal design was obtained after 15 iterations with a 2 dB reduction in the average interior sound pressure level. The ply angle orientation shifted from an initially symmetric lay-up to an unsymmetric lay-up in the final design.
On Friction Damping Modeling Using Bilinear Hysteresis Elements
Authors: Berger E. J. , Krousgrill C. M.
Published: July 2002

Massless bilinear hysteresis elements are often used to model frictional energy dissipation in dynamic systems. These quasi-static elements possess only two describing parameters, the damper stiffness and the force at which it slips. Bilinear hysteresis elements capture the qualitative nature of friction-damped forced response, but sometimes have difficulty with quantitative comparisons. This paper examines the performance of massless bilinear hysteresis elements as well as the role of damper mass in energy dissipation, and specifically evaluates its influence on the kinematic state of the damper (pure slip, stick-slip, pure stick). Differences between the massless and non-zero mass case are explored, as are the implications on both damper and system response. The results indicate that even small damper mass can have a qualitative effect on the system response, and provide advantages over the massless case. Further, we develop transition maps, describing damper response kinematics in the damper parameter space, which segment the space into two linear analysis regions (pure slip, pure stick) and one nonlinear analysis region (stick-slip). The results suggest non-zero mass dampers which are tuned as optimal vibration absorbers provide substantial resonance response attenuation and substantially reduce the size of the nonlinear analysis region in the damper parameter space.
Flow Field Simulations of a Gas Turbine Combustor
Authors: Barringer M. D. , Richard O. T. , Walter J. P. , Stitzel S. M. , Thole K. A.
Published: July 2002

The flow field exiting the combustor in a gas turbine engine is quite complex considering the presence of large dilution jets and complicated cooling schemes for the combustor liner. For the most part, however, there has been a disconnect between the combustor and turbine when simulating the flow field that enters the nozzle guide vanes. To determine the effects of a representative combustor flow field on the nozzle guide vane, a large-scale wind tunnel section has been developed to simulate the flow conditions of a prototypical combustor. This paper presents experimental results of a combustor simulation with no downstream turbine section as a baseline for comparison to the case with a turbine vane. Results indicate that the dilution jets generate turbulence levels of 15–18% at the exit of the combustor with a length scale that closely matches that of the dilution hole diameter. The total pressure exiting the combustor in the near-wall region neither resembles a turbulent boundary layer nor is it completely uniform putting both of these commonly made assumptions into question.
Flow Characteristics in Two-Leg Internal Coolant Passages of Gas Turbine Airfoils With Film-Cooling Hole Ejection
Authors: Chanteloup D. , Bo¨lcs A.
Published: July 2002

A study of flow in two stationary models of two-pass internal coolant passages is presented, which focuses on the flow characteristics in the 180-deg bend region, and downstream of the bend, where the flow is redeveloping. A stereoscopic digital PIV system measured all three velocity components simultaneously to obtain mean velocity, and turbulence quantities of the flow field. The coolant passage model consisted of two square passages, each having a 20 hydraulic diameter length, separated by a rounded-tip web of 0.2 passage widths, and connected by a sharp 180-deg bend with a rectangular outer wall. Ribs were mounted on the bottom and top walls of both legs, with a staggered arrangement, and at 45 deg to the flow. The rib height and spacing were 0.1 and 1.0 passage heights, respectively. The measurements were obtained for a flow condition, with a Reynolds number of 50,000. The geometries are similar in both sections except for one, which is equipped with extraction holes to simulate holes for film cooling. Two series of holes are placed solely in the bottom wall, four holes are located in the bend, and 12 in the downstream leg. The global extraction through the holes was set to 50% of the inlet massflow. This paper presents new measurements of the flow in the straight legs, as well as in the bend of the passage equipped with holes, detailed comparison of the flow upstream, inside and downstream of the bend region between both configurations, and the effects of extraction inside the cooling channels.
A Stability Solution for the Axial Contour-Turning Process
Authors: Reddy Rohit G. , Ozdoganlar O. Burak , Kapoor Shiv G. , DeVor Richard E. , Liu Xinyu
Published: July 2002

This paper presents an investigation of the stability variations in contour turning process. An equivalent chip-area formulation has been developed, and is used to model the dynamic machining forces. In order to establish a frequency domain solution for stability in the presence of geometric and structural variations along the tool path, the tool path is discretized into a finite number of portions, each of which possess constant geometric and structural properties. The stability solution developed here is capable of accommodating the effects of cutting conditions (axial and radial feed, depth of cut, and spindle speed), tooling geometry (lead angle and corner radius), workpiece geometry (contour tool path) and structural parameters (the mass, stiffness, damping ratio and orientation of the dominant mode). The stability solution is experimentally validated by machining a workpiece with a concave-convex contour combination. The solution has been applied to achieve productivity improvements via spindle speed regulation. A case study that includes contour turning of an aluminum wheel is also presented.
A Numerical Investigation of the Heat Transfer in a Parallel Plate Channel With Piecewise Constant Wall Temperature Boundary Conditions
Authors: Weigand B. , Schwartzkopff T. , Sommer T. P.
Published: July 2002

For turbulent flows in ducts, streamwise heat conduction effects within the flow can be important for low Prandtl number fluids (liquid metals). The paper presents a numerical investigation of the influence of axial heat conduction within the flow on the heat transfer for hydrodynamically fully developed flow. The calculations have been carried out for a semi-infinite heated section as well as for a heated section of finite length. Additionally, by considering different models for calculating the turbulent heat flux, the normally used assumption that the eddy diffusivity in axial and normal direction are the same was investigated.
Model for a multiple-step deep Si etch process
Authors: Rauf Shahid , Dauksher William J. , Clemens Stephen B. , Smith Kenneth H.
Published: July 2002

A multiple-step deep Si etch process involving separate etching and polymerization steps is often employed for fabrication of microelectromechanical systems, microfluidics devices, and other assorted deep structures in Si. An integrated plasma equipment-feature evolution model for this multiple-step deep Si etch process is described in this article. In the two-dimensional plasma equipment model, the etching (SF6/O2) and polymerization [octafluorocyclobutane(c-C4F8)] chemistries are separately simulated assuming steady-state conditions. The outputs of the equipment simulations are combined in a string-based feature profile evolution model to simulate the multiple-step deep Si etch process. In the plasma equipment models, detailed gas phase plasma chemistries including electron impact processes, ion–molecule reactions, and neutral chemistry have been considered for both the etching and polymerization gas mixtures. The plasma–surface interaction mechanisms in the feature profile evolution model are based on qualitative information available in literature and the correlation of modeling results with experimental data. Under the relevant operating conditions, F is assumed to be the primary Si etchant, film deposition in c-C4F8 is due to sticking of C, CF2, and C2F4 under ion bombardment, and the polymer is etched by energetic ions through physical sputtering. It is demonstrated that predictions of the resulting model are in close agreement with experiments. The validated model is used to understand the dynamics of the multiple-step deep Si etch process and how etching characteristics can be controlled using a variety of process parameters. Etching characteristics have been found to be quite sensitive to gas pressure, coil power, bias power, and relative step time during both etching and polymerization processes. The Si etch rate and feature sidewall angle are coupled to each other over a wide range of operating conditions.