Modelling of Rapid Transients

1994 ◽  
pp. 673-697
Author(s):  
A. P. Boldy
Keyword(s):  
Rapid Transients

Pepsinogen secretion from perifused frog peptic glands: Rapid transients detected with a modified pepsin assay

Life Sciences ◽  
1988 ◽  
Vol 42 (12) ◽  
pp. 1237-1244 ◽  
Author(s):  
Haruki Matsumoto ◽  
Kenneth E.J. Dickinson ◽  
Wayne Anderson ◽  
Basil I. Hirschowitz
Keyword(s):  
Pepsinogen Secretion ◽  
Rapid Transients

Development of Reliable NARX Models of Gas Turbine Cold, Warm and Hot Start-Up

2017 ◽  
Author(s):  
Hilal Bahlawan ◽  
Mirko Morini ◽  
Michele Pinelli ◽  
Pier Ruggero Spina ◽  
Mauro Venturini
Keyword(s):  
Gas Turbine ◽  
Training Data ◽  
Series Data ◽  
Data Sets ◽  
Control Logic ◽  
Start Up ◽  
Hot Start ◽  
Narx Models ◽  
Set Up ◽  
Rapid Transients

This paper documents the set-up and validation of nonlinear autoregressive exogenous (NARX) models of a heavy-duty single-shaft gas turbine. The considered gas turbine is a General Electric PG 9351FA located in Italy. The data used for model training are time series data sets of several different maneuvers taken experimentally during the start-up procedure and refer to cold, warm and hot start-up. The trained NARX models are used to predict other experimental data sets and comparisons are made among the outputs of the models and the corresponding measured data. Therefore, this paper addresses the challenge of setting up robust and reliable NARX models, by means of a sound selection of training data sets and a sensitivity analysis on the number of neurons. Moreover, a new performance function for the training process is defined to weigh more the most rapid transients. The final aim of this paper is the set-up of a powerful, easy-to-build and very accurate simulation tool which can be used for both control logic tuning and gas turbine diagnostics, characterized by good generalization capability.

Modeling of the Cavity Response to Rapid Transient Considering the Effect of Heat Transfer

2018 ◽  
Author(s):  
Shuiting Ding ◽  
Hang Yu ◽  
Tian Qiu ◽  
Chuankai Liu
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Heat Transfer Characteristics ◽  
Transient Responses ◽  
Transfer Characteristics ◽  
Thermal Boundary Conditions ◽  
Air System ◽  
Relative Errors ◽  
Low Dimensional ◽  
Rapid Transients

The internal air system, as one of the important subsystems of the aeroengine, is used to cooling and sealing, and plays a vital role in the safe operation of the engine. Especially in rapid transients, the complex dynamic response in air system may impose hazardous transition state loads on engine. Cavity is a component with pretty evident characteristics of transient in the air system due to the storage and release effects on the air. The flow and heat transfer characteristics of cavity should be made clear to precisely quantify the performance of the air system. The traditional study on cavity is based on the adiabatic assumption. However, the assumption is applicable to the transient of millisecond time scales physical phenomena in the air system, which is not usually common. Generally, the actual transition process is not instantaneous. Great discrepancies exist in the process of transition predicted by the adiabatic hypothesis compared with the practical process. The objective of this work is to propose a feasible method to solve the heat transfer issue throughout the transient process, which has not been settled by a proper method before, and develop a model for simulating the transient responses of the cavity with consideration of the heat transfer effect on the basis of the method. The model can predict transient responses under different thermal boundary conditions. Experiments have been developed for investigation of the charging process of the cavity. The thermal boundary can be controlled in the experiment, and the pressure and temperature responses of the cavity under different thermal boundary conditions have been analyzed. The non-dimensional numbers related to heat transfer characteristics were deduced by dimensional analysis, and the empirical formula of characteristics was proposed based on the experimental results. The non-adiabatic low-dimensional transient model of the cavity was established based on the heat transfer characteristics correlation. Results of transient responses calculated by non-adiabatic model were compared with the experimental data. It is found that both the transient responses of pressure and temperature agree well, with the maximum relative errors less than 2%. By comparison, the relative errors of pressure and temperature calculated by adiabatic model are about 8% and 12%, respectively. Meanwhile, the tendency of temperature response deviates from the actual process. Thus, the modeling method proposed is feasible and high-precision. The present work provides a technical method for establishing a low-dimensional model to describe the transient responses of the cavity with high accuracy, and supports the component-level modeling of the transient air system.

scholarly journals Assessment of water hammer effects on boiling water nuclear reactor core dynamics

2007 ◽  
Vol 22 (1) ◽  
pp. 18-33 ◽  
Author(s):  
Anis Bousbia-Salah
Keyword(s):  
Pressure Wave ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Reactor ◽  
Reactor Core ◽  
Water Hammer ◽  
Pressure Wave Amplitude ◽  
Sensitivity Studies ◽  
Rapid Transients ◽  
Complex Phenomena

Complex phenomena, as water hammer transients, occurring in nuclear power plants are still not very well investigated by the current best estimate computational tools. Within this frame work, a rapid positive reactivity addition into the core generated by a water hammer transient is considered. The numerical simulation of such phenomena was carried out using the coupled RELAP5/PARCS code. An over all data comparison shows good agreement between the calculated and measured core pressure wave trends. However, the predicted power response during the excursion phase did not correctly match the experimental tendency. Because of this, sensitivity studies have been carried out in order to identify the most influential parameters that govern the dynamics of the power excursion. After investigating the pressure wave amplitude and the void feed back responses, it was found that the disagreement between the calculated and measured data occurs mainly due to the RELAP5 low void condensation rate which seems to be questionable during rapid transients. .

scholarly journals Ultrafast electro-optic light with subcycle control

Science ◽  
2018 ◽  
Vol 361 (6409) ◽  
pp. 1358-1363 ◽  
Author(s):  
David R. Carlson ◽  
Daniel D. Hickstein ◽  
Wei Zhang ◽  
Andrew J. Metcalf ◽  
Franklyn Quinlan ◽  
...  
Keyword(s):  
High Speed ◽  
Near Infrared ◽  
Continuous Wave ◽  
Mode Locking ◽  
Light Sources ◽  
Electro Optic ◽  
High Pulse ◽  
Optical Cycle ◽  
Rapid Transients ◽  
And Control

Light sources that are ultrafast and ultrastable enable applications like timing with subfemtosecond precision and control of quantum and classical systems. Mode-locked lasers have often given access to this regime, by using their high pulse energies. We demonstrate an adaptable method for ultrastable control of low-energy femtosecond pulses based on common electro-optic modulation of a continuous-wave laser light source. We show that we can obtain 100-picojoule pulse trains at rates up to 30 gigahertz and demonstrate sub–optical cycle timing precision and useful output spectra spanning the near infrared. Our source enters the few-cycle ultrafast regime without mode locking, and its high speed provides access to nonlinear measurements and rapid transients.

Single Versus Dual Recycle System Dynamics of High Pressure Ratio, Low Inertia Centrifugal Compressor Stations

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
K. K. Botros
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Dynamic Instability ◽  
Pressure Ratio ◽  
Check Valve ◽  
Analytical Methodology ◽  
High Pressure Ratio ◽  
Compressor Surge ◽  
Rapid Transients ◽  
Single Versus

Compression systems are designed and operated in a manner to eliminate or minimize the potential for surge, which is a dynamic instability that is very detrimental to the integrity of the compressor unit. Compressor surge can occur when compressors are subjected to rapid transients such as those occurring following an emergency shutdown (ESD) or a power failure, which in turn, requires fast reaction. To prevent this from occurring, compressor stations are designed with single or dual recycle systems with recycle valves, which are required to open upon ESD. There has been extensive debate and confusion as to whether a single recycle or a dual recycle system is required and the circumstances and the conditions under which one system or the other must be used. This paper discusses this crucial design issue in detail and highlights the parameters affecting the decision to employ either system, particularly for high pressure ratio, low inertia compressors. Parameters such as gas volume capacitance (V) in the recycle path, compressor power train inertia, compressor performance characteristics, the recycle valve coefficient (Cv), prestroke and stroke time, and check valve dynamic characteristic are crucial in determining the conditions for dynamic instabilities. A simple analytical methodology based on the perturbation theory is developed that provides a first-cut analysis to determine if a single recycle system is adequate for a given compression system. The concept of an inertia number is then introduced with a threshold value that determines which recycle system to use. Techniques to circumvent compressor surge following ESD are discussed and their respective effectiveness are highlighted including when and if a delay in the fuel cutoff will be effective. An example of a case study with actual field data of a high pressure ratio centrifugal compressor employed in a natural gas compressor station is presented to illustrate the fundamental concept of single versus dual recycle systems.

Identification of the Mechanical Impedance at the Human Finger Tip

1997 ◽  
Vol 119 (1) ◽  
pp. 109-114 ◽  
Author(s):  
A. Z. Hajian ◽  
R. D. Howe
Keyword(s):  
Linear Model ◽  
Muscle Activation ◽  
Index Finger ◽  
Damping Ratio ◽  
Mechanical Impedance ◽  
Order Linear ◽  
Human Finger ◽  
Rapid Transients ◽  
Finger Tip ◽  
Tip Mass

Rapid transients were applied to the outstretched human index finger tip, which resulted in motion primarily at the metacarpophalangeal (MCP) joint in extension and in abduction. A second-order linear model was fit to approximately 20 milliseconds of the force and displacement data to determine the effective mechanical impedance at the finger tip. Ranges of mass, damping, and stiffness parameters were estimated over a range of mean finger tip force (2–20 N for extension, 2–8 N for abduction). Effective translational finger tip mass for each subject was relatively constant for force levels greater than 6 N for extension, and constant throughout the abduction trials. Stiffness increased linearly with muscle activation. The estimated damping ratio for extension trials was about 1.7 times the ratio for abduction.

A New Index to Evaluate the Potential Damage of a Surge Event: The Surge Severity Coefficient

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Enrico Munari ◽  
Mirko Morini ◽  
Michele Pinelli ◽  
Klaus Brun ◽  
Sarah Simons ◽  
...  
Keyword(s):  
Severity Index ◽  
Careful Analysis ◽  
Industrial Plants ◽  
Mechanical Parts ◽  
System Components ◽  
Aerodynamic Instability ◽  
Simulation Results ◽  
Pi Theorem ◽  
Potential Damage ◽  
Rapid Transients

Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system components due to the fact that it produces variable time-averaged mass flow and pressure. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge is usually prevented in industrial plants by means of anti-surge systems, which act as soon as surge occurs; however, some rapid transients or system upsets can lead the compressor to surge anyway. Despite the fact that surge can be classified as mild, classic, or deep, depending on the amplitudes and frequency of the fluctuations, operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is a common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor; thus, in these cases, inspections would not be required. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. In order to fill this gap, this paper proposes a final formulation of a surge severity index, which was only preliminarily formulated by the authors in a previous work. The preliminary form of this coefficient demonstrated some limitations, which are overcome in this paper. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of (i) the application of the Buckingham's Pi-theorem, and (ii) a careful analysis of the causative and restorative factors of surge. Finally, some simple practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.

Acoustic Based Rapid Blowout Mitigation in a Swirl Stabilized Combustor

2005 ◽  
Author(s):  
Shashvat Prakash ◽  
Suraj Nair ◽  
T. M. Muruganandam ◽  
Yedidia Neumeier ◽  
Tim Lieuwen ◽  
...  
Keyword(s):  
Real Time ◽  
Acoustic Signal ◽  
Equivalence Ratio ◽  
Constant Power ◽  
Event Frequency ◽  
Rapid Calculation ◽  
Power Setting ◽  
Proportional Derivative Controller ◽  
Extinction Events ◽  
Rapid Transients

This paper describes a method for efficiently detecting and preventing lean blow out (LBO) in a premixed, swirl stabilized combustor. The acoustic signal is processed to determine the real time LBO probability. This requires detection of localized extinction ‘events’ and rapid calculation of event frequency. As LBO probability increases, a proportional derivative controller actuates valves to redirect a fraction of the total fuel into a central, premixed pilot. The actuation increases the equivalence ratio in the stabilization region at a constant power setting and counters the flame lift associated with LBO. It is shown that the developed controller can prevent LBO even during rapid transients in equivalence ratio, φ.

scholarly journals Rapid Transients Originating from Thermonuclear Explosions in Helium White Dwarf Tidal Disruption Events

2020 ◽  
Vol 890 (2) ◽  
pp. L26 ◽  
Author(s):  
Kojiro Kawana ◽  
Keiichi Maeda ◽  
Naoki Yoshida ◽  
Ataru Tanikawa
Keyword(s):  
White Dwarf ◽  
Tidal Disruption ◽  
Rapid Transients
Sign in / Sign up

Export Citation Format

Share Document