Cavitation Phenomena and Performance Implications in Archimedes Flow Turbines

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Jacob D. Riglin ◽  
William C. Schleicher ◽  
Alparslan Oztekin
Keyword(s):  
Rotation Rate ◽  
Single Phase ◽  
Cavitation Number ◽  
Flow Coefficient ◽  
Archimedean Spiral ◽  
Rotation Rates ◽  
A Value ◽  
And Performance ◽  
Onset Of Cavitation ◽  
Blade Geometry

Cavitation produces undesirable effects within turbines, such as noise, decreases in efficiency, and structural degradation of the device. Two microhydro turbines incorporating Archimedean spiral blade geometries were investigated numerically for cavitation effects using computational fluid dynamics (CFD). Separate blade geometries, one with a uniform blade pitch angle and the other with a 1.5 power pitch, were modeled using the Schnerr–Sauer cavitation model. The method used to determine where cavitation occurs along the blade and within the flow involved varying inlet flow rates and the rotation rate of the blade. Cavitation analysis was conducted locally as well as globally, using both cavitation number and Thoma number. The cavitation number was used to correlate the single-phase to the multiphase results for rotation rates of 250 and 500 rpm, allowing for the single-phase simulations to be used to determine where the onset of cavitation occurs. It was determined that cavitation occurred at the exit of the blade at a flow coefficient of approximately 0.33 for the 1.5 pitch blade geometry, while the uniform blade geometry had a value of 1.35. When the rotation rate was reduced to 250 rpm, cavitation occurred at a flow coefficient of 0.72. From the simulations at both rotation rates, it was determined that both geometry and rotation rate have a significant effect on the onset of cavitation and water vapor inception within the flow field. As the rotation rate of the turbine decreases, the onset of cavitation will be prolonged to larger flow coefficients. As the flow coefficient increased beyond the value at which the onset of cavitation occurs, the intensity of cavitation increases and efficiency drops of up to 20% were experienced by the turbines. Based on the net positive suction head required in the system and the available head in the system, the cavitation results were validated. It was determined that the inception cavitation number, Cai, where the onset of cavitation occurs is approximately −1.51.

THE USE OF HISTORICAL DATA IN ACCOUNTING RESEARCH: THE CASE OF THE AMERICAN SUGAR REFINING COMPANY

1997 ◽  
Vol 24 (2) ◽  
pp. 1-24 ◽  
Author(s):  
Robert Bricker ◽  
Kevin Brown
Keyword(s):  
Capital Market ◽  
Historical Data ◽  
Abnormal Returns ◽  
Deep Understanding ◽  
Historical Record ◽  
Historical Period ◽  
Financial Condition ◽  
A Value ◽  
Time Period ◽  
And Performance

In 1908, the American Sugar Refining Company (ASR) reversed its long-held policy of secrecy as to its financial condition and performance. Prior work, applying contemporary capital market methods to ASR security price data of that period, has suggested a value to ASR shareholders of this policy reversal. This paper examines the historical record of that time and presents additional evidence on this matter, particularly in terms of identifying potentially confounding events occurring during the period under study. The results of this analysis suggest a difficulty in attributing observed abnormal returns to ASR's secrecy policy reversal on the basis of the results obtained from applying capital markets methods. This analysis is useful for scholars interested in applying modern capital market methods to historical data. It highlights the significance of the possible effects of contemporaneous historical events, focuses attention on the importance of a deep understanding of the historical period studied, and suggests a value in combining historical and empirical-markets methods to gain a richer understanding of the events and conditions in the time period under study.

scholarly journals Design and Performance Evaluation of a Single-Phase Driven Ultrasonic Motor Using Bending-Bending Vibrations

Micromachines ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 853
Author(s):  
Dongmei Xu ◽  
Wenzhong Yang ◽  
Xuhui Zhang ◽  
Simiao Yu
Keyword(s):  
Single Phase ◽  
Oblique Line ◽  
Ultrasonic Motor ◽  
Vibration Modes ◽  
Bending Vibrations ◽  
Bending Vibration ◽  
Output Performance ◽  
Resonance Frequencies ◽  
And Performance ◽  
Line Trajectory

An ultrasonic motor as a kind of smart material drive actuator has potential in robots, aerocraft, medical operations, etc. The size of the ultrasonic motor and complex circuit limits the further application of ultrasonic motors. In this paper, a single-phase driven ultrasonic motor using Bending-Bending vibrations is proposed, which has advantages in structure miniaturization and circuit simplification. Hybrid bending vibration modes were used, which were excited by only single-phase voltage. The working principle based on an oblique line trajectory is illustrated. The working bending vibration modes and resonance frequencies of the bending vibration modes were calculated by the finite element method to verify the feasibility of the proposed ultrasonic motor. Additionally, the output performance was evaluated by experiment. This paper provides a single-phase driven ultrasonic motor using Bending-Bending vibrations, which has advantages in structure miniaturization and circuit simplification.

Flow Coefficient Evaluation of Poppet Valves Used in Reciprocating Compressors for LDPE

2008 ◽  
Author(s):  
Enzo Giacomelli ◽  
Massimo Schiavone ◽  
Fabio Manfrone ◽  
Andrea Raggi
Keyword(s):  
Pressure Drop ◽  
Time Pressure ◽  
Experimental Tests ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Operating Life ◽  
High Fatigue ◽  
Strongly Connected ◽  
And Performance ◽  
Poppet Valves

Poppet valves have been used for a long time for very high pressure reciprocating compressors, as for example in the case of Low Density Polyethylene. These applications are very critical because the final pressure can reach 350 MPa and the evaluation of the performance of the machines is strongly connected to the proper operation and performance of the valve itself. The arrangement of cylinders requires generally a certain compactness of valve to withstand high fatigue stresses, but at the same time pressure drop and operating life are very important. In recent years the reliability of the machines has been improving over and over and the customers’ needs are very stringent. Therefore the use of poppet valves has been extended to other cases. In general the mentioned applications are heavy duty services and the simulation of the valves require some coefficients to be used in the differential equations, able to describe the movement of plate/disk or poppet and the flow and related pressure drop through the valves. Such coefficients are often determined in an experimental way in order to have a simulation closer to the real operating conditions. For the flow coefficients it is also possible today to use theoretical programs capable of determining the needed values in a quick and economical way. Some investigations have been carried out to determine the values for certain geometries of poppet valves. The results of the theory have been compared with some experimental tests. The good agreement between the various methods indicates the most suitable procedure to be applied in order to have reliable data. The advantage is evident as the time necessary for the theoretical procedure is faster and less expensive. This is of significant importance at the time of the design and also in case of a need to provide timely technical support for the operating behavior of the valves. Particularly for LDPE, the optimization of all the parameters is strongly necessary. The fatigue stresses of cylinder heads and valve bodies have to match in fact with gas passage turbulence and pressure drop, added to the mechanical behavior of the poppet valve components.

Toward constraining Saturn's rotation rate by interior modeling

2021 ◽  
Author(s):  
Nadine Nettelmann ◽  
Jonathan J. Fortney
Keyword(s):  
Broad Spectrum ◽  
Rotation Rate ◽  
Rotation Period ◽  
Outer Planet ◽  
Fall Meeting ◽  
Density Profiles ◽  
A Value ◽  
Periodic Signals ◽  
Under Construction ◽  
Even Harmonics

<p>The rotation rate of the outer planet Saturn is not well constrained by classical measurements of periodic signals [1]. Recent and diverse approaches using a broad spectrum of Cassini and other observational data related to shape, winds, and oscillations are converging toward a value about 6 to 7 minutes faster than the Voyager rotation period.<br>Here we present our method of using zonal wind data and the even harmonics J<sub>2</sub> to J<sub>10</sub> measured during the Cassini Grand Finale tour [2] to infer the deep rotation rate of Saturn. We assume differential rotation on cylinders and generate adiabatic density profiles that match the low-order J<sub>2</sub> and J<sub>4</sub><br>values. Theory of Figures to 7th order is applied to estimate the differences in the high-order moments J<sub>6 </sub>to J<sub>10</sub> that may result from the winds and the assumed reference rotation rate. Presented results are preliminary as the method is under construction [3].</p><p>[1] Fortney, Helled, Nettelmann et al, in: 'Saturn in the 21st century', Cambridge U Press (2018)<br>[2] Iess, Militzer, Kaspi, Science 364:2965 (2019)<br>[3] Nettelmann, AGU Fall Meeting, P066-0007 (2020)</p><p> </p>

Using Modeling and Simulation Techniques to Improve the Accountability and the Performance of Human Resource Management

2018 ◽  
pp. 75-112
Author(s):  
Florea Nicoleta Valentina ◽  
Manea Marinela Daniela
Keyword(s):  
Human Capital ◽  
Human Resources ◽  
Organizational Performance ◽  
Simulation Techniques ◽  
A Value ◽  
Long Run ◽  
Level Data ◽  
Strategic Role ◽  
And Performance ◽  
The Impact

The analysis of human resources function and its contribution to obtain performance dates back to the 1920s. Now, the HR is an equal partner on the board of the companies, having a strategic role in obtaining performance, thus we try to show that compensating appropriately, the human capital it will be motivated to obtain performance. This paper examines the two different visions of different managers in which the human capital is perceived as a major cost for organization and the others which perceive it as an investment on long run. In this article, we analyse the impact could have the direct costs of human capital on individual and organizational performance using samples of some variables from European level, data between 2005-2016. Data used for the different years were analysed using simulation methods. Findings of this study show consistency with the theory in the filed, bringing a value in motivation and accountability of human capital and performance obtained through human capital.

Influence of shape and material of rotor bars on performance characteristics of single-phase self-excited induction generators

2019 ◽  
Vol 38 (4) ◽  
pp. 1235-1244 ◽  
Author(s):  
Aleksander Leicht ◽  
Krzysztof Makowski
Keyword(s):  
Single Phase ◽  
General Purpose ◽  
Performance Characteristics ◽  
Induction Generator ◽  
Content Type ◽  
Operating Range ◽  
Induction Generators ◽  
Stable Operating ◽  
Rotor Cage ◽  
And Performance

Purpose The purpose of the paper is to present an analysis of an influence of shape and material of rotor bars on the process of self-excitation and performance characteristics of single-phase, self-excited induction generator (SP-SEIG). Design/methodology/approach The presented analysis is based on the results of transient simulations of SP-SEIG performed with the use of field-circuit model of the machine. Four various shapes of the rotor bars and two different conductor materials were investigated. The results for the base model with rounded trapezoidal rotor slots were validated by measurements. Findings An improvement of the performance characteristics – the extension of the stable operating range of the generator – was obtained for rectangular copper rotor bars. The improvement is the result of strong skin effect in the squirrel rotor cage. Application of round rotor slots results in shorter time of voltage build-up during the self-excitation of the generator caused by less apparent deep bar effect in round bars. Originality/value The originality of the paper is the application of the copper rotor cage in the single-phase, self-excited induction generator. Its use is beneficial, as it allows for extension of the range of stable operating range. The results may be used for designing new constructions of the single-phase, self-excited induction generators, as well as the constructions based on general purpose single-phase induction motors.

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