Lixiang Zhang

Nonlinear hydro turbine model having a surge tank.

This article models a hydro turbine based on the dynamic description of the hydraulic system having a surge tank and elastic water hammer. The dynamic of the hydraulic system is transformed from transfer function form into the differential equation model in relative value. This model is then combined with the motion equation of the main servomotor to form the nonlinear model of the hydro turbine, in which the power of the hydro turbine is calculated using algebraic equation. A new control model is thus proposed in which the dynamic of the surge tank is taken as an additional input of control items. As such, the complex hydraulic system is decomposed into a classical one penstock and one machine model with an additional input control. Therefore, the order of the system is descended. As a result, the feasibility of the system is largely improved. The simulated results show that the additional input of the surge tank is effective and the proposed method is realizable.

Dynamical mode transitions of simply supported double-walled carbon nanotubes based on an elastic shell model

The nonlinear vibration behaviors of double-walled carbon nanotubes (DWCNTs) are investigated based on Donnell’s cylindrical shell model with van der Waals (vdW) forces between the inner and outer tubes. The harmonic balance method is used to analyze the relationship between the amplitudes and the frequencies of natural vibrations of the tubes. Numerical analyses are carried out to understand the effects of vdW forces and nonlinearity on the carbon nanotubes (CNTs). The results show that the radial vibrational modes of the inner and outer tubes of simply supported DWCNTs have twice dynamical mode transitions as the frequency increases. The transitions correspond to twice the noncoaxial vibrations, which play a critical role in the electronic and transport properties of CNTs.

Building and Analysis of Hydro Turbine Dynamic Model with Elastic Water Column

The structure of dynamic models of nonlinear hydro turbine with elastic water column is studied in this paper. The nonlinear differential equations for hydraulic system (NDE-HS) are derived based on transfer function model of it. The dynamic model I of hydro turbine is built by combining NDE-HS with the algebraic equation of hydro turbine torque. By means of except of transfer coefficient, the differential equation of hydro turbine torque is derived and combines with NDE-HS, the dynamic model II is built. Simulation is done with actual hydroelectric plant, simulation results show that dynamic responses of two type models are almost same, and the dynamic of hydro turbine is determined by hydraulic system. Furthermore, the nonlinear differential-algebraic model for hydro turbine is given, which is a reduce-order system and includes inner energy loss characteristic.

High Order Generator Hamiltonian Model Included AVR and PSS Energy Function

Take the typical SCR excitation system including AVR(auto voltage regulator) and PSS(power system stabilizer) as an example, AVR and PSS branches were converted into their equivalent circuits. The controller energy function was derived by circuit parameters, and constituted in circuit parameters of AVR and PSS branch , then, the controller energy function was added to the Hamiltonian function of generator object-oriented system, and composed the total energy function of system. by proper transformation, generator Hamiltonian model standard form included AVR and PSS were derived, The model including characteristic parameters of structure matrix and damping matrix laid a foundation for studying the interaction mechanism between controller included AVR/ PSS and generator object-oriented system. Meanwhile, a new method for description of the energy function of controller is proposed, finally, combining with the model derived, the paper analysis the structural relationship and interaction preliminary, The results show that structure connection and damping characteristics are consistent with practical system.

Hamiltonian model of shafting lateral vibration for hydro turbine generating sets

From basic dynamical characteristics and energy composition of shafting, the differential equation model of shafting vibration is built, in which various additional forces acted on the shafting of hydro turbine generating sets are taken as additional input controls. And then differential equation model is transformed into the generalized Hamiltonian control model of hydro turbine generating sets shafting. In this model, additional forces acted on shafting are taken as input inspire of system, and be used to research their effects on shafting motion. Further, the additional forces can be merged into the system matrix of Hamiltonian model, and then physical conceptions of the structure and damping matrix of Hamiltonian system can be employed to research the coupling dynamics mechanism between shafting and additional forces. Proposed model is form concise and good commonality.

Improvement Rotor Angle Oscillation of Hydro Turbine Generating Sets Based on Hamiltonian Damping Injecting Method

The rotor angle stability of generator is basic to hydro turbine generating sets (HTGS) and power systems stabilization. Firstly, an approximate design method is proposed to solve the difficulty in application for Hamiltonian damping injection method. Secondly, the Hamiltonian model of HTGS is built by connecting Hamiltonian model of nonlinear hydro turbine and generator. Adding the relative factors of rotor angle in damping matrix and adopting this design method, two-input control laws of the excitation and governor are derived to stabilize system. At last, the effects of relative factor are simulated under the HTGS regulated active power. Simulation results indicate that the method can reduce rotor angle oscillation in weak damping effectively.

Efficiency limit factor analysis for the Francis-99 hydraulic turbine

The energy loss in hydraulic turbine is the most direct factor that affects the efficiency of the hydraulic turbine. Based on the analysis theory of inner energy loss of hydraulic turbine, combining the measurement data of the Francis-99, this paper calculates characteristic parameters of inner energy loss of the hydraulic turbine, and establishes the calculation model of the hydraulic turbine power. Taken the start-up test conditions given by Francis-99 as case, characteristics of the inner energy of the hydraulic turbine in transient and transformation law are researched. Further, analyzing mechanical friction in hydraulic turbine, we think that main ingredients of mechanical friction loss is the rotation friction loss between rotating runner and water body, and defined as the inner mechanical friction loss. The calculation method of the inner mechanical friction loss is given roughly. Our purpose is that explore and research the method and way increasing transformation efficiency of water flow by means of analysis energy losses in hydraulic turbine.

Rotating Turbulent Flow Simulation with LES and Vreman Subgrid-Scale Models in Complex Geometries

The large eddy simulation (LES) method based on Vreman subgrid-scale model and SIMPIEC algorithm were applied to accurately capture the flowing character in Francis turbine passage under the small opening condition. The methodology proposed is effective to understand the flow structure well. It overcomes the limitation of eddy-viscosity model which is excessive, dissipative. Distributions of pressure, velocity, and vorticity as well as some special flow structure in guide vane near-wall zones and blade passage were gained. The results show that the tangential velocity component of fluid has absolute superiority under small opening condition. This situation aggravates the impact between the wake vortices that shed from guide vanes. The critical influence on the balance of unit by spiral vortex in blade passage and the nonuniform flow around guide vane, combined with the transmitting of stress wave, has been confirmed.

Simulation Method of Low Frequency Oscillation Signal on Studying Generating Units Oscillation

To study the oscillation characteristic of generating units under low frequency oscillation and give an reference for controller design, a simulation method is proposed to simulate the low frequency oscillation signal. According to the oscillation characteristics in generating units-side, the rotor angle oscillation (RAO) is decomposed into steady and additional parts. The additional RAO is simulated with sine signal- and is divided into three types, uniform amplitude, damped and random oscillation. Differential equations of RAO included oscillation characteristics are given correspondingly, which combine with other equation of generating units to compose the simulation model. In this way, oscillation amplitude and angular speed can be adjusted, so the oscillation characteristic of generating units can be simulated overall, and use to easy.

Hamiltonian Model of Hydro Turbine with Sharing Common Conduit

To bring the hydro turbine and hydraulic system into the theory frame of the generalized Hamiltonian and study the dynamic mechanism of its operation and control, the model of its Hamiltonian system is studied in this paper. Based on the differential equation model of hydro turbine decomposed hydraulic dynamics with sharing common conduit, by constructing the Hamiltonian function of hydraulic turbine, the nonlinear model of hydro turbine is converted to Hamiltonian system by adopting orthogonal decomposition realization, and it is realized into Hamiltonian dissipative forms by decomposing the structure matrix and designing the dissipative feedback. The variation of dissipative structure, feedback equivalence and energy flow in built Hamiltonian model are studied, the energy flows of Hamiltonian are consistent with actual system in description of generalized energy. Simulation indicates that the Hamiltonian function contains detailed main information of energy change of hydraulic turbine in transient, and is feasible.