Modeling of the Dynamic Response of a Pelton Turbine Hydroelectric Plant

2011 ◽  
Author(s):  
P. Pennacchi ◽  
S. Chatterton ◽  
A. Vania
Keyword(s):  
Experimental Data ◽  
Hydroelectric Plant ◽  
Low Frequency ◽  
Pressure Waves ◽  
Surge Tank ◽  
Electric Generator ◽  
Pelton Turbine ◽  
Speed Governor ◽  
Hydroelectric Unit ◽  
Water Inertia

The paper presents a detailed numerical model of the dynamics of a Pelton turbine installed in a hydroelectric plant. The model considers in detail the Pelton turbine with all the electromechanical subsystems, such as the main speed governor, the controller and the servoactuator of the turbine nozzle, and the electric generator. In particular it reproduces the effects of pipe elasticity in the penstock, the water inertia and the water compressibility on the turbine behaviour. The dynamics of the surge tank on low frequency pressure waves is also modeled together with the main governor speed loop and the position controllers of the nozzle needle actuators and of the hydraulic electrovalve. Model validation has been made by means of experimental data acquired during some starting tests after a partial revamping of a hydroelectric unit, which involved also the control system of the hydraulic actuators but not the nozzles. The model is used in order to identify the cause of the oscillations of the electric power mainly ascribed to the backlash of the nozzle needle system.

Resonance in a mathematical model of baroreflex control: arterial blood pressure waves accompanying postural stress

2005 ◽  
Vol 288 (6) ◽  
pp. R1637-R1648 ◽  
Author(s):  
Peter E. Hammer ◽  
J. Philip Saul
Keyword(s):  
Blood Pressure ◽  
Mathematical Model ◽  
Blood Volume ◽  
Low Frequency ◽  
Pressure Waves ◽  
Central Blood Volume ◽  
Arterial Baroreflex ◽  
Arterial Blood ◽  
Gain Margin ◽  
The Stability

A mathematical model of the arterial baroreflex was developed and used to assess the stability of the reflex and its potential role in producing the low-frequency arterial blood pressure oscillations called Mayer waves that are commonly seen in humans and animals in response to decreased central blood volume. The model consists of an arrangement of discrete-time filters derived from published physiological studies, which is reduced to a numerical expression for the baroreflex open-loop frequency response. Model stability was assessed for two states: normal and decreased central blood volume. The state of decreased central blood volume was simulated by decreasing baroreflex parasympathetic heart rate gain and by increasing baroreflex sympathetic vaso/venomotor gains as occurs with the unloading of cardiopulmonary baroreceptors. For the normal state, the feedback system was stable by the Nyquist criterion (gain margin = 0.6), but in the hypovolemic state, the gain margin was small (0.07), and the closed-loop frequency response exhibited a sharp peak (gain of 11) at 0.07 Hz, the same frequency as that observed for arterial pressure fluctuations in a group of healthy standing subjects. These findings support the theory that stresses affecting central blood volume, including upright posture, can reduce the stability of the normally stable arterial baroreflex feedback, leading to resonance and low-frequency blood pressure waves.

Investigations of the Optical Properties of LaNi5 and LaNi4.5Sn0.5

2013 ◽  
Vol 321-324 ◽  
pp. 495-498 ◽  
Author(s):  
Dong Chen ◽  
Chao Xu
Keyword(s):  
Experimental Data ◽  
Refractive Index ◽  
Optical Properties ◽  
Density Functional ◽  
Low Frequency ◽  
Potential Method ◽  
Frequency Region ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Pseudo Potential

The reflectivity, loss function, refractive index, extinction coefficient and dielectric function of the LaNi5and LaNi4.5Sn0.5intermetallic compounds are investigated through the plane-wave pseudo-potential method based on the density functional theory. The effects of Sn impurity are discussed and some interesting features are found in the low frequency region. Some important optical properties such as static dielectric constant and static refractive index are obtained. The equation [n (0)]2=ε1(0)is satisfied according to our calculation, which indicates that our results are correct and reasonable. Nevertheless, the calculated results need to be testified in the future due to the lack of experimental data.

Development of a Methodology for the Evaluation of Motion Sickness Incidence in Railways

2013 ◽  
Author(s):  
Claudio Braccesi ◽  
Filippo Cianetti ◽  
Renzo Scaletta
Keyword(s):  
Experimental Data ◽  
Theoretical Model ◽  
Motion Sickness ◽  
Evaluation Method ◽  
Low Frequency ◽  
Comparison With Experimental Data

The present paper illustrates an evaluation method developed by the authors to quantify the index of motion sickness incidence (MSI) in railways motion conditions. This index is formerly defined in literature to quantify diseases coming from low frequency motions (kinetosis). The proposed method, suggested as alternative to the only one existing in reference norm, involves PCT index, well known in railways context, and weighting curves for accelerometric signals, which are also specified in railways regulations. The approach of the method, consistent with the theoretical model, developed by the authors themselves in previous works, allows to obtain MSI index versus time and/or track progressive distance. The model is validated through comparison with experimental data available in literature and with measures recorded and obtained on regular trains during tests performed in Slovenia (EU).

Interaction of Point Defects in Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 115-122
Author(s):  
J. H. Bilgram ◽  
H. Gränicher
Keyword(s):  
Experimental Data ◽  
Dielectric Properties ◽  
Temperature Dependence ◽  
Point Defects ◽  
Low Frequency ◽  
Defect Concentration ◽  
Dielectric Measurements ◽  
Long Time ◽  
Nmr Techniques ◽  
Bjerrum Defect

AbstractThe interaction of point detects in ice has been neglected for a long time. Experimental data obtained from dielectric measurements on HF-doped crystals stimulated a new evaluation of the possibility of an interaction between Bjerrum defects and ions. In a previous paper it has been shown that this leads us to assume the existence of aggregates of Bjerrum defects and ions. In this paper these aggregates and Bjerrum defects are used to explain the dielectric properties of ice, especially the temperature dependence of the product of the high and low frequency conductivity σ0σ∞.The interaction of Bjerrum defects and impurity molecules leads to a dependence of the concentration of frenkel pairs on Bjerrum-defect concentration. At HF concentrations above the native Bjerrum-defect concentration the formation of a Frenkel pair is enhanced. This leads to the fast out-diffusion which has been studied in highly doped crystals by means of NMR techniques.

scholarly journals The Tangential Force Affecting the Radial Baffles in a Stirred Vessel: Analysis of the Macro-instability Related Component

10.14311/450 ◽  
2003 ◽  
Vol 43 (4) ◽  
Author(s):  
P. Hasal ◽  
I. Fořt ◽  
J. Kratěna
Keyword(s):  
Experimental Data ◽  
Spectral Analysis ◽  
Tangential Force ◽  
Low Frequency ◽  
Frequency Component ◽  
Relative Magnitude ◽  
Tangential Component ◽  
Vertical Position ◽  
Total Force ◽  
Rushton Turbine

Experimental data obtained by measuring the tangential component of the force affecting radial baffles in a flat-bottomed cylindrical mixing vessel stirred with a Rushton turbine impeller is analysed. Spectral analysis of the experimental data demonstrated the presence of its macro-instability (MI) related low-frequency component embedded in the total force. Two distinct dimensionless frequencies (both directly proportional to the impeller speed of rotation N) of the occurence of the MI component were detected: a lower frequency of approximately 0.025N and a higher frequency of about 0.085N. The relative magnitude QMI of the MI-related component of the total tangential force was evaluated by a combination of proper orthogonal decomposition (POD) and spectral analysis. The values of magnitude QMI varied in the interval [rom approximately 0.05 to 0.30. The magnitude QMI takes maximum values at low Reynolds number values (in laminar and transitional regions). In the turbulent region (ReM >20000) the QMI value is low and practically constant. The dependence oj the QMI values on vertical position in the vessel is only marginal. The results suggest that the magnitude of the MI component of the force is significantly influenced by the liquid viscosity and density.

Oscillations of a moderately underexpanded choked jet impinging upon a flat plate

1996 ◽  
Vol 315 ◽  
pp. 267-291 ◽  
Author(s):  
Chih-Yu Kuo ◽  
Ann P. Dowling
Keyword(s):  
Experimental Data ◽  
Flat Plate ◽  
Pressure Ratio ◽  
Feedback Mechanism ◽  
Pressure Waves ◽  
Stagnation Flow ◽  
Stability Threshold ◽  
Shock Position ◽  
The Stability ◽  
Plate Distance

The oscillation of a moderately underexpanded choked jet impinging upon a flat plate is investigated both analytically and numerically. The feedback mechanism between oscillations of the standoff-shock and the plate is clarified. Pressure waves produced by the motion of the shock are reflected by the plate. In addition, oscillations in the shock position lead to downstream entropy fluctuations, which generate pressure waves as they are convected through the stagnation flow near the plate. A linear stability analysis is used to investigate the stability threshold and frequencies of oscillation, as a function of jet pressure ratio and nozzle-to-plate distance. The analytical predictions are compared to results from a numerical simulation and to the experimental data of Powell (1988) and Mørch (1963, 1964).

Mycotoxins in Coffee

1980 ◽  
Vol 63 (6) ◽  
pp. 1282-1285 ◽  
Author(s):  
Colette Levi
Keyword(s):  
Experimental Data ◽  
Low Frequency ◽  
Toxin Production ◽  
Green Coffee ◽  
Extremely Low Frequency ◽  
Mycotoxin Contamination ◽  
Green Coffee Beans ◽  
Coffee Beans ◽  
Roasting Process ◽  
Low Levels

Abstract This report reviews studies concerning the susceptibility of green coffee beans to mycotoxin contamination. Included are investigations on normal mold flora, toxin production in inoculated beans, effect of experimental roasting on aflatoxin, ochratoxin, and sterigmatocystin, and survey on the presence of these toxins in commercial green coffee. Because of the extremely low frequency of findings, the low levels of toxins, and the experimental data showing 70–80% destruction by the roasting process of toxin added to green coffee, further study on this topic has been discontinued.

Oscillatory Flow of a Magnetic Fluid in a Pipe at Low Frequency Range Under a Magnetic Field: Phase Difference of Pressure

2003 ◽  
Author(s):  
Kunio Shimada ◽  
Shigemitsu Shuchi ◽  
Shinichi Kamiyama
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Phase Difference ◽  
Mass Concentration ◽  
Oscillatory Flow ◽  
Low Frequency ◽  
Nonuniform Distribution ◽  
Straight Pipe ◽  
Number Range ◽  
Steady Magnetic Field

We made on numerical analysis of phase difference between pressure along the pipe axis and given oscillatory flow velocity in an straight pipe under a nonuniform steady magnetic field. In the analysis, a few cases under the assumption of numerical condition were conducted on: the first is taking into account the least compressibility of the fluid with using the obtained experimental data of the bulk modulus, the second taking into account the nonuniform distribution of mass concentration of particles, and the thrid taking into account the aggregation with the number of aggregated particles proposing as a prorate spheroid. By considering the three effects of the least compressibility and the nonuniform distribution of mass concentration, the aggregation as a prorate spheroid, the phase difference varies quantitatively at the lowest Womersley number range. And then, the numerical results were compared with the experimental data.

scholarly journals Velocity of radio waves in glaciers as an indicator of their hydrothermal state, structure and regime

1993 ◽  
Vol 39 (132) ◽  
pp. 373-384 ◽  
Author(s):  
Yu. Ya. Macheret ◽  
M. Yu. Moskalevsky ◽  
E.V. Vasilenko
Keyword(s):  
Experimental Data ◽  
Radio Wave ◽  
Water Content ◽  
Low Frequency ◽  
Wide Angle ◽  
Radio Waves ◽  
State Structure ◽  
Mountain Ridge ◽  
Wave Velocities

AbstractThe results of measurements of radio-wave velocities (RWV) by wide-angle reflection (WAR) methods in the temperate Abramov Glacier in the Alai Mountain Ridge and the “two-layered” sub-polar Fridtjovbreen and Hansbreen on Svalbard using a low-frequency (2–13 MHz) radar are considered and discussed. The experimental data obtained and the data from the literature show that the values of RWV could be a good indicator of the hydrothermal state of glaciers. As such, these data enable the identification of cold, temperate and transitional (two-layered) glaciers, and can be used for estimation of the water content in glaciers and changes in the hydrothermal state.

Sign in / Sign up

Export Citation Format

Share Document