An Energy-Equivalent Simplified Model for Lateral Nonlinear Vibrations of Coupled Water Turbine Generator Set Shaft-Foundation System

The traditional whole finite element method (WFEM[1]) has several shortcomings, including that it has too many degrees of freedom so the execution is not efficient and is difficult to solve in nonlinear dynamic analysis. In this paper, a novel simplified modeling approach is proposed to investigate the lateral nonlinear vibration characteristics of coupled water turbine generator set shaft-foundation system (CSFS[2]). The simplified coupled model is generated in two stages. First, a more reasonable simplified model for foundation subsystem considering coupling with each other is constructed to simulate the lateral vibrations of guide bearing foundations in hydropower house. Based on the response spectra of WFEM of hydropower house and a constructed energy error objective function, the optimal equivalent parameters of the simplified foundation model are then determined by using the genetic algorithm. Second, considering actions of various nonlinear factors and the pulsating water pressure acting on turbine runner, a nonlinear dynamic differential equations of CSFS based on Lagrange equation are derived. The nonlinear dynamic responses of CSFS using the optimal equivalent model are also compared with the field test data. It is demonstrated that the method proposed to develop the equivalent model is more efficient and more convenient in capturing the nonlinear dynamic behavior of CSFS. In addition, this energy-equivalent model is more adaptable to the stochastic uncertainty and frequency band variation in hydropower station system. Some novel dynamic laws and inner mechanism of the coupled system are also revealed further based on the proposed model. Footnotes: [1] WFEM: whole finite element method[2] CSFS: coupled water turbine generator set shaft-foundation system

Study on FSI Analysis Method of a Large Hydropower House and Its Vortex-Induced Vibration Regularities

The working principle of a large hydropower station is to guide the high-pressure water flow to impact the turbine to rotate and generate electricity. The high-pressure water flow impacts the turbine blades, which forms complex high-speed eddy currents in the spiral case and the draft tube and causes complicated vortex-induced vibration problems. Traditionally used harmonic response methods and dynamic time-history analysis methods are difficult to reflect this complex fluid-solid dynamic coupling problem. In this paper, the bidirectional fluid-structure interaction (FSI) simulation analysis theory for a large hydropower house is studied, and the analysis methods of geometric simulation, mechanical simulation, and vibration energy transmission path simulation are presented. A large-scale 3D fluid-hydraulic machinery-concrete structure coupled model of a hydropower house is established to study the vortex-induced vibration mechanism and coupled vibration law during transient unit operation. A comparison of the fluid results against the in-site data shows good agreement. Structural responses of vibration displacement, velocity, and acceleration reveal coupled regularity of hydraulic machinery-concrete structure-fluid during blades rotating periods, and it comes to the conclusion that the turbine blade rotation is the main vibration source of the hydropower house. The research results can provide a scientific basis for the design and safe operation of the hydropower house.

Vibration transmission path identification in a hydropower house based on a time-delayed transfer entropy method

This article aims to explore the vibration transmission path in the hydropower house using the time-delayed transfer entropy method. A three-dimensional fluid-concrete structure-hydraulic machinery coupling simulation model of the Xiangjiaba hydropower house was established, and the vibration acceleration and equivalent stress of the structure were calculated in the time domain based on the two-way iterative fluid-structure interaction method. The characteristic indexes of information transmission were quantitatively presented, including the rate of information transmission, transmission path contribution, to describe the vibration energy transmission paths and transmission characteristics of different vibration variables as well as different directions of the same variable in the hydropower house. The study indicates that the vertical acceleration can identify more abundant vibration transmission paths, and the lower bracket contributes most to the vibration transmission of the powerhouse. The research outcome can provide a scientific basis for structural optimization, vibration attenuation, and isolation design of the hydropower house.

Research on Unsteady Hydraulic Features of a Francis Turbine and a Novel Method for Identifying Pressure Pulsation Transmission Path

It is of significant value to understand the unsteady hydraulic features and pressure pulsation transmission path in the flow channel through a turbine for providing technical support for turbine design and optimization, as well as laying a foundation for analysis of the stability and the coupled vibration of the hydropower house. In this paper, a three-dimensional mechanics–hydraulics–concrete structure coupled numerical model was established to accurately simulate Francis hydraulic machinery, including the high-rotating turbine runner and fixed guide vane, the unsteady flowing water, the structure of the entire flow channel, as well as the dynamic interaction between them. Turbulent hydraulic features of flow condition and pressure pulsation in design operation were explored using the detached eddy simulation (DES) turbulence model. Then, a novel method was proposed to identify the fluid pressure pulsation transmission path based on the time-delayed transfer entropy method and wavelet theory. On basis of time and frequency analysis of pressure calculation results, investigation into identification of pressure pulsation transmission path was performed using the method of traditional transfer entropy and the method adopted in this paper. The pressure pulsation transmission features in the entire flow channel were revealed during operation of the large-scale Francis turbine. The research method and results could not only lay a basis for exploring the structural vibration regularity of the hydropower house but also provide a scientific reference for vibration reduction design of the hydropower house.

Whiplash Effect on Hydropower House During an Earthquake

The mutation of mass and stiffness between the superstructure and substructure of a hydropower station can lead to the whiplash effect on the hydropower house during an earthquake. This paper explains the mechanism of the whiplash effect based on the theory of structural dynamics. A Chinese hydropower house was taken as a test case to discuss the whiplash effect on this type of structures. An integral finite element model and partial models of the hydropower house were established according to its structural features, arrangement forms and loading features. The dynamic response and the whiplash effect of the hydropower house were investigated by direct time integration using the Newmark method.