Numerical Simulation Of Transient Processes Research Articles

Numerical simulation of transient processes for pumped-storage power station with fixed and variable speed units

The pumped-storage power stations (PSPSs) with variable speed units (VSUs) have been emerging in recent years, and the research on the transient processes of those PSPSs is of great significance. In this paper, the transient processes of a PSPS with four units, i.e. three fixed speed units (FSUs) and one VSU, sharing one tunnel are numerically simulated under the conditions of large fluctuation and small fluctuation. Firstly, combining the calculation method of hydraulic transient processes and the basic equations of pump turbine, doubly-fed induction motor (DFIM) and governor, a hydraulic-mechanical-electrical coupling model of PSPS is established. Secondly, the data of an actual PSPS is substituted into the model and the corresponding parameters are set. Then, the transient processes of typical conditions of large fluctuation and small fluctuation are simulated respectively. Finally, according to the numerical simulation results, the characteristics of the transient processes of PSPS with three FSUs and one VSU are analyzed. The results show that, under large fluctuation conditions, whether the initial operating states of FSUs and VSU are consistent or not, the transient processes are similar. Under small fluctuation conditions, the VSU can adjust the active power to meet the grid demand more quickly than the FSUs.

Improved transfer function method for flexible simulation of hydraulic-mechanical-electrical transient processes of hydro-power plants

The hydraulic-mechanical-electrical coupling dynamics of hydropower plants during transient processes is a key issue in engineering practice. Numerical simulation of transient process could provide support for practical operation of hydropower plants and avoid dangerous working conditions, indirectly increasing the unit operation time and improving economic benefits. Numerous previous studies used the transfer function method (TFM) for modelling and simulation of hydropower plants, but many previous models are oversimplified and cannot simulate some complicated transient processes. To solve this problem, a nonlinear and flexible model of hydropower plant is developed on Simulink in this work. TFM is adopted to model the waterway system with complicated hydraulic components, and an improved scheme of TFM is recommended. Quantitative comparison of time-domain and frequency-domain simulations demonstrates the accuracy of the improved TFM in simulating the water hammer in the waterway system. Besides, the improved TFM is applied to combine with complicated electrical modules on Simulink, simulating hydraulic-mechanical-electrical coupling dynamics under hydraulic disturbance and three-phase fault. In conclusion, the method developed in this paper has advantages of accuracy, flexibility, and expansibility, enabling deeper understanding and refined simulation for transient processes of hydropower plants. The hydraulic-mechanical-electrical coupling model can be used to simulate a variety of working conditions in engineering practice and support future research on the dynamic characteristics of hydropower plants.

Electric heater mathematical model for cyber-physical systems

The article discusses the heat and mass transfer dynamic model for an electric heater with lumped parameters, which allows transient processes simulation for the main influences. The proposed model is recommended to be used in cyber-physical systems for forecasting and evaluating the effectiveness of control systems integrated into a single information management system. The developed model can be used by specialists for the analysis and synthesis of control systems for balanced ventilation systems or industrial air conditioners. As an example, a numerical simulation of transient processes along the action main channels for an electric heater HE 36/2 manufactured by VTS CLIMA was carried out. The significant advantage of the proposed model is the possibility for using it for the synthesis and analysis of multidimensional control systems.

Numerical simulation of transient processes in propeller shaft straining under ice loads

Object and purpose of research. The object of the research is the shaftline of an icebreaker and ice-going vessels, the purpose is to develop an algorithm for determining the loads for calculating the strength of the shafts of icebreakers and icegoing vessels under ice loads in a nonlinear dynamic setting and determining the dynamic magnification factor.
 Materials and methods. The study is based on finite element method (FEM).
 Main results. As a result of numerical analysis, the magnification factors of ice loads acting on the propeller shaft when vessel moves in an ice field up to 4 m thick are investigated.
 Conclusion. The research results can be used to calculate the fatigue strength of the icebreakers and ice-going vessels shaftlines.

TIME-VARIANT MODEL OF HEAT-AND-MASS EXCHANGE FOR STEAM HUMIDIFIER

The dynamical model of heat-mass exchange for a steam humidifier with lumped parameters, which can be used for synthesis of control systems by inflowing-exhaust ventilation installations, or industrial complexes of artificial microclimate, is considered. A mathematical description that represents the dynamical properties of a steam humidifier concerning the main channels of control and perturbation is presented. Numerical simulation of transient processes for the VEZA KCKP-20 humidification chamber to the influence channels was carried out. The achieved dynamical model of a humidification chamber can be the basis for the synthesis of automatic control systems and simulation of transient states. A significant advantage of the obtained mathematical model in the state space is the possibility of synthesis and analysis of a multidimensional control system.

Simulation of Generator Transients with Asymmetry of Stator Phase Circuits

Transient processes of a synchronous machine operating on a load with a delta connection circuit are considered. A method is proposed for numerical simulation of transient processes of a synchronous machine with the possibility of taking into account the asymmetry of the stator winding. The model was verified by comparing the results of the calculation of generator transients with an asymmetrical stator winding, obtained using the developed model and using the MATLAB Simulink tools

INVESTIGATION OF THE DYNAMICS OF NONLINEAR MECHANICAL SYSTEMS WITH LONG POWER LINES THROUGH DIGITAL MODELING

Many of the mechanisms used in industry contain input and output links connected by long lines of force. Increasing the efficiency and service life of mechanical systems with long lines is of great importance for the country's economy. For a more rational use of these devices, it is important to maintain these operating modes with maximum accuracy, usually including the required speed of the actuator and the voltage in the lines. Such parameters can spontaneously change depending on the operating conditions of the system. In the presence of various influences, similar tasks to determine the marked regimes and parameters indicating the need for their change can be solved only with the help of the corresponding theory and research methods. The article presents the problems and the method of studying two-tier mechanical systems with an infinite number of degrees of freedom on the basis of the equations of momentum and moment of momentum in differential form. Transformations with the use of well-known wave equations are proposed, which made it possible to explicitly take into account the oscillations of the speeds of motion and stresses in the force lines of mechanical systems when describing dynamic processes. The solution of systems of partial differential equations is given using the Laplace transform, which made it possible to obtain general equations of motion and, after some simplifications, proceed to ordinary differential equations that take into account the dynamic features of systems with distributed parameters. The modernized Runge-Kutta method obtained solutions and carried out numerical simulation of transient processes in the hydraulic drive, the results of which have good convergence with full-scale experiments.

The Investigation of Thermodynamic Processes in Pulsed Coils with Crowbar Circuit

The analysis of thermodynamic processes in pulsed coils with crowbar circuit and resistive ballast is described. Great overheating due to Joule heating takes place in pulsed coil during operation. The influence of crowbar circuit on generated pulse shape and coil overheating is analyzed. The model was carried out using Matlab Simulink software and applied for numerical simulation of transient processes that took place in winding of pulsed coil. The numerical simulation of pulsed currents and temperature rise were carried out for different values of resistive ballast using the same experimental equipment and laboratory conditions. Depending on resistance of the crowbar resistive ballast fall time of generated pulse has changed at wide range and as a result temperature rise in Cu-Nb windings of pulsed coil has changed too. Using 0,2 – 0,4 Ohm ballast temperature rise decreased drastically and overheating due to Joule heating has been avoided even without initial cooling. Applied model of transient processes took place in pulsed coils with crowbar circuit and resistive ballast was verified experimentally and acceptable compliance of experimental and numerically simulated results was achieved. Ill. 6, bibl. 11 (in English; abstracts in English, Russian and Lithuanian).

Research on numerical simulation and protection of transient process in long-distance slurry transportation pipelines

The calculation of water-hammer pressure phenomenon of single-phase liquid is already more mature for a pipeline of uniform characteristics, but less research has addressed the calculation of slurry water hammer pressure in complex pipelines with slurry flows carrying solid particles. In this paper, based on the developments of slurry pipelines at home and abroad, the fundamental principle and method of numerical simulation of transient processes are presented, and several boundary conditions are given. Through the numerical simulation and analysis of transient processes of a practical engineering of long-distance slurry transportation pipeline system, effective protection measures and operating suggestions are presented. A model for calculating the water impact of solid and fluid phases is established based on a practical engineering of long-distance slurry pipeline transportation system. After performing a numerical simulation of the transient process, analyzing and comparing the results, effective protection measures and operating advice are recommended, which has guiding significance to the design and operating management of practical engineering of longdistance slurry pipeline transportation system.

Numerical simulation of transient processes in hydroturbines

A method for calculation of unsteady 3D turbulent flows in hydro turbines of power plants developed for simulation of the transient processes is presented herein. The method is based on joint solution to the Reynolds-averaged Navier—Stokes equations for incompressible fluid flow written for moving mesh, the equation of runner rotation and the system of 1D equations describing propagation of elastic hydraulic shock in the flow domain. The exchange in flow parameters between the penstock and hydro turbine regions is considered in this approach. Results of transient processes simulation are presented for several modes: start-up to the turbine regime, instantaneous load shedding, and output power decrease. Comparison with experimental data is performed.

Numerical Simulation of Transient Process for Corrosion Environment in Coating Crevice with Cathodic Protection

Numerical Simulation of Transient Process for Corrosion Environment in Coating Crevice with Cathodic Protection

Numerical simulation and investigation of induction through‐heaters in dynamic operation mode

PurposeBecause of their widespread use in industry, induction through‐heaters of various metal products must be of high effectiveness not only in “quasi” steady‐state operation but in different transient modes as well. Nowadays, they are usually designed to provide the required characteristics in “quasi” steady‐state operation mode mainly. The purpose of this paper is to examine numerical simulation of transient processes in induction through‐heating lines generally and investigate dynamic temperature fields during the first start of the heaters particularly.Design/methodology/approachThe research methodology is based on coupled numerical electromagnetic and thermal analyses using FEM approach. ANSYS simulations are supported with the developed tools for imitation of mass transfer effects in continuous induction heating lines.FindingsThe results show that transient temperature fields in the heated strip or slab significantly differ from their “quasi” steady‐state descriptions. Local temperature variations acquired in longitudinal as well as transverse flux induction heaters during the first start have been predicted.Practical implicationsThe received results can be used for design of induction through‐heaters and improvement of their characteristics in dynamic operation modes.Originality/valueInvestigation of dynamic characteristics of the heaters in dynamic modes can be only done by numerical modelling based on special algorithms providing a time loop additional to coupling between electromagnetic and thermal analyses. Such algorithms have been developed and used for investigation of two types of induction installations: through‐heaters of cylindrical billets for forging and heating lines of strip or thin slab for rolling mills.

Nonlinear-optical vacuum ultraviolet generation at maximum atomic coherence controlled by a laser-induced Stark chirp of two-photon resonance

A novel scheme is analyzed for efficient generation of vacuum ultraviolet radiation through four-wave mixing processes assisted by the Stark chirp of two photon resonance. In this three-laser technique, a delayed-pulse of strong off-resonant infrared radiation sweeps the laser-induced Stark shift of a two-photon transition and facilitates maximum two-photon coherence induced by the second ultraviolet laser. A judiciously delayed third pulse beats with this coherence and generates short-wavelength radiation. A numerical simulation of transient processes, which ensure maximum coherence, including those leading to Stark-chirped rapid adiabatic passage, is presented. Potential high power and energy conversion efficiency of the weak long-wavelength radiation to the VUV range is shown for a difference-frequency scheme based on parametric amplification of this signal and strong four-wave coupling at maximum atomic coherence.

Numerical simulation of transient processes in a 170 GHz/1 MW gyrotron for ITER

We present the results of numerical simulation of transient processes at the leading edge of the accelerating voltage pulse, when the excitation of parasitic oscillations is most probable. The results obtained show the possibility of establishing stable one-mode high-efficiency generation in a 170 GHz/1 MW gyrotron for ITER.

Half-implicit difference scheme for numerical simulation of transient processes in semiconductor devices

A half-implicit, absolutely stable difference scheme for numerical solution of the fundamental equation which describe the transient processes in semiconductor devices is proposed. The calculations of transient processes in a transistor device and I 2 L device illustrate the potential of the method.

Numerical simulation of transient processes in 2-D bipolar transistors

A numerical method for the solution of the fundamental equations which describe the transient processes in 2-D bipolar semiconductor devices is proposed. The method extends the algorithm previously used by the authors [1,2] for simulation of 1-D problems. Some numerical results for a 2-D problem are presented and compared with results of 1-D simulation.

Comparison of different methods for numerical simulation of transient processes in bipolar semiconductor devices

Comparison of different methods for numerical simulation of transient processes in bipolar semiconductor devices