Spool Hydraulic Stiffness and Flow Force Effects in Electrohydraulic Servo-Valves

1987 ◽  
Vol 201 (3) ◽  
pp. 193-199 ◽  
Author(s):  
H A Arafa ◽  
M Rizk
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Linear Feedback ◽  
Magnetic Saturation ◽  
Stable Operation ◽  
Experimental Assessment ◽  
Servo Valve ◽  
Supply Pressure ◽  
Wide Range ◽  
Good Agreement

This paper deals with an analytical and experimental assessment of the flow force effects on electrohydraulic servo-valve steady state characteristics. The system mathematical model is derived, and special consideration is given to non-linearity of the feedback wire stiffness and magnetic saturation of the armature. The ‘spool hydraulic stiffness’ is defined and expressed in terms of the servo-valve parameters and supply pressure to allow clear interpretation of the nature of flow force effects. Experimental results of spool displacement decrement due to flow force versus net displacement are in good agreement with the predicted performance in a wide range of input current up to almost full magnetic saturation. The results provide evidence, on an alternative basis, of the non-linear feedback behaviour. Correlation is also made between flow force and limits of stable operation, and an expression is derived for the maximum allowable supply pressure.

Combined cycle dynamics

2003 ◽  
Vol 217 (3) ◽  
pp. 247-258 ◽  
Author(s):  
F. M. Mansour ◽  
A. M. Abdul Aziz ◽  
S. M. Abdel-Ghany ◽  
H. M. El-shaer
Keyword(s):  
Steady State ◽  
Differential Equations ◽  
Combined Cycle ◽  
Stable Operation ◽  
Algebraic Equations ◽  
State Equations ◽  
Combined Cycle Plant ◽  
Fast Settling ◽  
Operational Data ◽  
Good Agreement

A mathematical model describing the dynamic behaviour of each major component of the combined cycle is presented. The formulae are deduced from continuity, momentum, energy, and state equations. Partial differential equations (PDEs) are discretized to algebraic equations by using the implicit backward-central finite difference scheme and then solved by iteration. Explicit-Euler's integration method is applied to other differential equations (DEs). A multi-element control system is implemented to investigate its effect on the combined cycle's dynamic response. The simulation results are compared with the design and steady-state operational data of the unit number 4 in Cairo South Combined Cycle Power Plant, showing good agreement. The dynamic results prove the effectiveness of the multi-element control strategy to control the combined cycle plant with fast settling time, neglected steady-state error, and moderate overshoot or undershoot while assuring a stable operation under sudden changes of load.

Development and Validation of a Steady-State Mathematical Model for the Physicochemical Processing of Biopolymers by Reactive Extrusion

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Marie-Amélie De Ville d'Avray ◽  
Arsène Isambert ◽  
Stéphane Brochot ◽  
Pierre Ferchaud
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Chemical Reactions ◽  
Chemical Engineering ◽  
Research Work ◽  
Hybrid Approach ◽  
Reactive Extrusion ◽  
Modelling And Simulation ◽  
Wide Range ◽  
Twin Screw

In reactive extrusion, the extruder is used as a solvent-free continuous chemical reactor able to process highly viscous materials. The chemical transformation of biopolymers by reactive extrusion appears as a very promising technology. Although punctual applications in this field have already been achieved on a laboratory or pilot scale, the amount of work to carry out is still considerable. A wide range of reactions and raw materials may be explored, and the reactions achieved on a laboratory scale have to be optimized and transposed to an industrial scale. Process modelling and simulation constitute useful tools for process understanding, development, optimization and scale-up. Although reactive extrusion modelling has interested many authors, it still remains a challenge because of the complex geometry and the strong coupling between operating parameters, flow conditions, material rheological behavior and reaction kinetics. A steady-state mathematical model for a biopolymer oxidation process by reactive extrusion is here proposed. The model is based on a hybrid approach combining chemical engineering methods and simplified continuum mechanics laws. The combination of these two approaches enables to simplify the calculations related to chemical reactions while ensuring a predictive character. The flexible structure of the model enabled its implementation within a global process simulator. A method to minimize the amount of experimental data required for model parameter adjustment is also presented. The model was validated by experiments conducted on a semi-pilot corotating twin-screw extruder. Even if it may be refined, the model proposed already constitutes a useful tool for later research work dealing with the development, modelling and simulation of chemical reactions in corotating twin-screw extruders.

Simulation of C1 fluxes in cyanobacteria: comparison between the carboxysome hypothesis and the equilibrium proposal

1997 ◽  
Vol 75 (12) ◽  
pp. 2117-2130 ◽  
Author(s):  
Christophe Salon ◽  
David Thomas Canvin
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Kinetic Constants ◽  
Experimental Conditions ◽  
Extracellular Medium ◽  
Blue Green Algae ◽  
Permeability Coefficients ◽  
Inorganic Species ◽  
Wide Range ◽  
Entire Cell

Inorganic carbon fluxes were simulated by a mathematical model using an equilibrium hypothesis for a wide range of conditions in a closed system composed of air-grown cells of Synechococcus UTEX 625 in a reaction vessel connected to a mass spectrometer. The metabolic scheme took into account the input fluxes of CO2 and HCO3− transport into the cells, the output fluxes of CO2 and HCO3− efflux, the diversion of Q toward the formation of the internal C2 pool, and photosynthetic CO2 fixation. The equations expressed the variation in concentration of each inorganic species outside and inside the cell as a function of time. The input fluxes were previously characterized by their kinetic constants (K1/2 and Vm) both during initial uptake occurring upon illumination of the cells and under steady-state photosynthesis conditions. The efflux rates of the various Ci species from the cells were investigated under a wide variety of experimental conditions. Using these efflux rates, the permeability coefficients of the cell for CO2 and HCO3− were calculated previously. Using the kinetic constants for CO2 and HCO3− transport, the permeability coefficients of the cell for CO2 and HCO3− and the geometrical characteristics of the cells, the model simulated precisely the [HCO3−]/[CO2] ratio and the [CO2] and [O2] changes in the extracellular medium as well as the rate of filling of the internal Ci pool under various conditions. Accurate fitting of experimental data with calculated values were possible only when the intracellular Ci species were assumed to be in equilibrium throughout the entire cell volume. Results are discussed and compared with those given by previous hypotheses. Key words: Synechococcus UTEX 625, blue green algae, cyanobacteria, mathematical model, active CO2 transport, active HCO3− transport, steady state, photosynthesis, Ci concentrating mechanism.

The Mathematical Modelling of Hydrostatic Pumps and Motors

1984 ◽  
Vol 198 (3) ◽  
pp. 165-174 ◽  
Author(s):  
D McCandlish ◽  
R E Dorey
Keyword(s):  
Mathematical Model ◽  
Test Data ◽  
Operating Conditions ◽  
Performance Tests ◽  
Hydraulic Systems ◽  
Wide Range ◽  
Comprehensive Performance ◽  
Real Performance ◽  
Classical Models ◽  
Good Agreement

Accurate mathematical models of hydrostatic pumps and motors are required in the synthesis and analysis of hydraulic systems. Increasingly the models are used in computer simulation work where the performance of the machines must be represented over a wide range of operating conditions. Examination of test data has shown significant differences in the real performance characteristics of hydrostatic machines compared to the characteristics predicted by classical models based on simple linear theory. This paper describes these differences and shows the way that the characteristics can change with different designs of machine. A mathematical model is developed which may be adapted to describe the wide range of characteristics associated with the different designs. This model has shown good agreement with test data. Recommendations are made for more comprehensive performance tests to provide the data required for more accurate models.

Spectroscopic Studies of Asparaginyl-tRNA Synthetase from Entamoeba histolytica

2019 ◽  
Vol 26 (6) ◽  
pp. 435-448
Author(s):  
Priyanka Biswas ◽  
Dillip K. Sahu ◽  
Kalyanasis Sahu ◽  
Rajat Banerjee
Keyword(s):  
Circular Dichroism ◽  
Steady State ◽  
Entamoeba Histolytica ◽  
Protein Concentration ◽  
Trna Synthetase ◽  
Solvent Exposure ◽  
Steady State Fluorescence ◽  
State Process ◽  
Wide Range ◽  
Circular Dichroïsm

Background: Aminoacyl-tRNA synthetases play an important role in catalyzing the first step in protein synthesis by attaching the appropriate amino acid to its cognate tRNA which then transported to the growing polypeptide chain. Asparaginyl-tRNA Synthetase (AsnRS) from Brugia malayi, Leishmania major, Thermus thermophilus, Trypanosoma brucei have been shown to play an important role in survival and pathogenesis. Entamoeba histolytica (Ehis) is an anaerobic eukaryotic pathogen that infects the large intestines of humans. It is a major cause of dysentery and has the potential to cause life-threatening abscesses in the liver and other organs making it the second leading cause of parasitic death after malaria. Ehis-AsnRS has not been studied in detail, except the crystal structure determined at 3 Å resolution showing that it is primarily α-helical and dimeric. It is a homodimer, with each 52 kDa monomer consisting of 451 amino acids. It has a relatively short N-terminal as compared to its human and yeast counterparts. Objective: Our study focusses to understand certain structural characteristics of Ehis-AsnRS using biophysical tools to decipher the thermodynamics of unfolding and its binding properties. Methods: Ehis-AsnRS was cloned and expressed in E. coli BL21DE3 cells. Protein purification was performed using Ni-NTA affinity chromatography, following which the protein was used for biophysical studies. Various techniques such as steady-state fluorescence, quenching, circular dichroism, differential scanning fluorimetry, isothermal calorimetry and fluorescence lifetime studies were employed for the conformational characterization of Ehis-AsnRS. Protein concentration for far-UV and near-UV circular dichroism experiments was 8 µM and 20 µM respectively, while 4 µM protein was used for the rest of the experiments. Results: The present study revealed that Ehis-AsnRS undergoes unfolding when subjected to increasing concentration of GdnHCl and the process is reversible. With increasing temperature, it retains its structural compactness up to 45ºC before it unfolds. Steady-state fluorescence, circular dichroism and hydrophobic dye binding experiments cumulatively suggest that Ehis-AsnRS undergoes a two-state transition during unfolding. Shifting of the transition mid-point with increasing protein concentration further illustrate that dissociation and unfolding processes are coupled indicating the absence of any detectable folded monomer. Conclusion: This article indicates that GdnHCl induced denaturation of Ehis-AsnRS is a two – state process and does not involve any intermediate; unfolding occurs directly from native dimer to unfolded monomer. The solvent exposure of the tryptophan residues is biphasic, indicating selective quenching. Ehis-AsnRS also exhibits a structural as well as functional stability over a wide range of pH.

scholarly journals Separate Universe calibration of the dependence of halo bias on cosmic web anisotropy

2020 ◽  
Vol 499 (3) ◽  
pp. 4418-4431 ◽  
Author(s):  
Sujatha Ramakrishnan ◽  
Aseem Paranjape
Keyword(s):  
Dark Matter ◽  
High Precision ◽  
Gaussian Distribution ◽  
Initial Perturbation ◽  
Analytical Framework ◽  
Web Environment ◽  
Wide Range ◽  
Galaxy Assembly ◽  
Very High ◽  
Good Agreement

ABSTRACT We use the Separate Universe technique to calibrate the dependence of linear and quadratic halo bias b1 and b2 on the local cosmic web environment of dark matter haloes. We do this by measuring the response of halo abundances at fixed mass and cosmic web tidal anisotropy α to an infinite wavelength initial perturbation. We augment our measurements with an analytical framework developed in earlier work that exploits the near-lognormal shape of the distribution of α and results in very high precision calibrations. We present convenient fitting functions for the dependence of b1 and b2 on α over a wide range of halo mass for redshifts 0 ≤ z ≤ 1. Our calibration of b2(α) is the first demonstration to date of the dependence of non-linear bias on the local web environment. Motivated by previous results that showed that α is the primary indicator of halo assembly bias for a number of halo properties beyond halo mass, we then extend our analytical framework to accommodate the dependence of b1 and b2 on any such secondary property that has, or can be monotonically transformed to have, a Gaussian distribution. We demonstrate this technique for the specific case of halo concentration, finding good agreement with previous results. Our calibrations will be useful for a variety of halo model analyses focusing on galaxy assembly bias, as well as analytical forecasts of the potential for using α as a segregating variable in multitracer analyses.

scholarly journals Research on Zero-Voltage Ride Through Control Strategy of Doubly Fed Wind Turbine

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2287
Author(s):  
Kaina Qin ◽  
Shanshan Wang ◽  
Zhongjian Kang
Keyword(s):  
Wind Turbine ◽  
Wind Power ◽  
Control Strategy ◽  
Large Scale ◽  
Sliding Mode ◽  
Stable Operation ◽  
Wide Range ◽  
Dc Bus ◽  
Doubly Fed ◽  
Zero Voltage

With the rapid increase in the proportion of the installed wind power capacity in the total grid capacity, the state has put forward higher and higher requirements for wind power integration into the grid, among which the most difficult requirement is the zero-voltage ride through (ZVRT) capability of the wind turbine. When the voltage drops deeply, a series of transient processes, such as serious overvoltage, overcurrent, or speed rise, will occur in the motor, which will seriously endanger the safe operation of the wind turbine itself and its control system, and cause large-scale off-grid accident of wind generator. Therefore, it is of great significance to improve the uninterrupted operation ability of the wind turbine. Doubly fed induction generator (DFIG) can achieve the best wind energy tracking control in a wide range of wind speed and has the advantage of flexible power regulation. It is widely used at present, but it is sensitive to the grid voltage. In the current study, the DFIG is taken as the research object. The transient process of the DFIG during a fault is analyzed in detail. The mechanism of the rotor overcurrent and DC bus overvoltage of the DFIG during fault is studied. Additionally, the simulation model is built in DIgSILENT. The active crowbar hardware protection circuit is put into the rotor side of the wind turbine, and the extended state observer and terminal sliding mode control are added to the grid side converter control. Through the cooperative control technology, the rotor overcurrent and DC bus overvoltage can be suppressed to realize the zero-voltage ride-through of the doubly fed wind turbine, and ensure the safe and stable operation of the wind farm. Finally, the simulation results are presented to verify the theoretical analysis and the proposed control strategy.

scholarly journals Identification of DC Thermal Steady-State Differential Inductance of Ferrite Power Inductors

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3854
Author(s):  
Salvatore Musumeci ◽  
Luigi Solimene ◽  
Carlo Stefano Ragusa
Keyword(s):  
Steady State ◽  
Input Voltage ◽  
Switching Frequency ◽  
Ohmic Losses ◽  
Steady State Temperature ◽  
Wide Range ◽  
Average Current ◽  
Power Inductors ◽  
Saturable Inductor ◽  
Thermal Steady State

In this paper, we propose a method for the identification of the differential inductance of saturable ferrite inductors adopted in DC–DC converters, considering the influence of the operating temperature. The inductor temperature rise is caused mainly by its losses, neglecting the heating contribution by the other components forming the converter layout. When the ohmic losses caused by the average current represent the principal portion of the inductor power losses, the steady-state temperature of the component can be related to the average current value. Under this assumption, usual for saturable inductors in DC–DC converters, the presented experimental setup and characterization method allow identifying a DC thermal steady-state differential inductance profile of a ferrite inductor. The curve is obtained from experimental measurements of the inductor voltage and current waveforms, at different average current values, that lead the component to operate from the linear region of the magnetization curve up to the saturation. The obtained inductance profile can be adopted to simulate the current waveform of a saturable inductor in a DC–DC converter, providing accurate results under a wide range of switching frequency, input voltage, duty cycle, and output current values.

scholarly journals Analysis of Dynamic Response of a Two Degrees of Freedom (2-DOF) Ball Bearing Nonlinear Model

2021 ◽  
Vol 11 (2) ◽  
pp. 787
Author(s):  
Bartłomiej Ambrożkiewicz ◽  
Grzegorz Litak ◽  
Anthimos Georgiadis ◽  
Nicolas Meier ◽  
Alexander Gassner
Keyword(s):  
Mathematical Model ◽  
Degrees Of Freedom ◽  
Ball Bearing ◽  
Hertzian Contact ◽  
Two Degrees Of Freedom ◽  
Wide Range ◽  
Shape Errors ◽  
Nonlinear Features ◽  
Fourier Transform Phase ◽  
Hertzian Contact Theory

Often the input values used in mathematical models for rolling bearings are in a wide range, i.e., very small values of deformation and damping are confronted with big values of stiffness in the governing equations, which leads to miscalculations. This paper presents a two degrees of freedom (2-DOF) dimensionless mathematical model for ball bearings describing a procedure, which helps to scale the problem and reveal the relationships between dimensionless terms and their influence on the system’s response. The derived mathematical model considers nonlinear features as stiffness, damping, and radial internal clearance referring to the Hertzian contact theory. Further, important features are also taken into account including an external load, the eccentricity of the shaft-bearing system, and shape errors on the raceway investigating variable dynamics of the ball bearing. Analysis of obtained responses with Fast Fourier Transform, phase plots, orbit plots, and recurrences provide a rich source of information about the dynamics of the system and it helped to find the transition between the periodic and chaotic response and how it affects the topology of RPs and recurrence quantificators.

SET-VALUED PERFORMANCE APPROXIMATIONS FOR THE QUEUE GIVEN PARTIAL INFORMATION

2020 ◽  
pp. 1-23
Author(s):  
Yan Chen ◽  
Ward Whitt
Keyword(s):  
Steady State ◽  
Decay Rate ◽  
Waiting Time ◽  
Partial Information ◽  
Upper And Lower Bounds ◽  
Interarrival Time ◽  
Limited Information ◽  
Wide Range ◽  
The Mean ◽  
Third Moment

In order to understand queueing performance given only partial information about the model, we propose determining intervals of likely values of performance measures given that limited information. We illustrate this approach for the mean steady-state waiting time in the $GI/GI/K$ queue. We start by specifying the first two moments of the interarrival-time and service-time distributions, and then consider additional information about these underlying distributions, in particular, a third moment and a Laplace transform value. As a theoretical basis, we apply extremal models yielding tight upper and lower bounds on the asymptotic decay rate of the steady-state waiting-time tail probability. We illustrate by constructing the theoretically justified intervals of values for the decay rate and the associated heuristically determined interval of values for the mean waiting times. Without extra information, the extremal models involve two-point distributions, which yield a wide range for the mean. Adding constraints on the third moment and a transform value produces three-point extremal distributions, which significantly reduce the range, producing practical levels of accuracy.

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