Hydropower House Research Articles

Insights into the nonlinear dynamic characteristics of a water turbine generator set considering the coupled effects of a fractional-order broadband foundation

The analysis of the coupled shaft-foundation system (CSFS) of a water turbine generator set is an extremely complicated task owing to its structural complexity and inherent nonlinear broadband dynamic characteristics. Thus, the coupling relationships of the CSFS remain unclear. The broadband vibration of the foundation subsystem has an evident influence on the vibration of the shaft subsystem of the unit; however, for the analysis of the dynamic characteristics of the water turbine generator, an overly complicated foundation can be reasonably simplified. To this end, this paper reports the development of novel energy-equivalent broadband modeling approaches to investigate the nonlinear vibration characteristics of CSFS. First, a relatively traditional integer-order lumped parameter model of the foundation subsystem was constructed, and its parameters were determined by fitting the response spectra obtained from an accurate hydropower house model. To improve the narrow-frequency limitation of the integer-order model and account for random disturbances, a novel fractional-order broadband modeling method is proposed. The advantage of the proposed fractional-order equivalent foundation model is that it can simultaneously reveal the broadband characteristics of complex structures at low frequencies of less than 1 Hz to high frequencies of hundreds of Hz with a single degree of freedom. Finally, coupled dynamic equations for the fractional-order CSFS model were derived and solved by considering the actions of various nonlinear factors and hydraulic pulsation excitation. A comparison of the dynamic responses of the CSFS with field test data demonstrated the effectiveness and practicability of the proposed modeling approaches. The results of the integer- and fractional-order CSFS models provide insights into the abundant dynamic laws and inner mechanisms of the nonlinear coupled dynamic system. Furthermore, they provided a reliable theory for the design and stability analysis of a hydropower unit, considering the varied vibrations of the coupled foundation.

Study on Vibration-Transmission-Path Identification Method for Hydropower Houses Based on CEEMDAN-SVD-TE

The analysis of the vibration-transmission path is one of the keys to the vibration control and safety monitoring of a hydropower house, and the vibration source of the hydropower house is complex, making it more difficult to analyze the vibration-transmission path. In order to accurately identify the transmission path of the vibration in a hydropower house, an identification method for the vibration-transmission path based on CEEMDAN-SVD-TE is presented in this paper. First of all, this paper verifies that the CEEMDAN-SVD-TE method has higher effectiveness and is superior to the single transfer-entropy (TE) algorithm in information-transmission-direction identification; secondly, based on the measured field-vibration data, CEEMDAN-SVD noise-reduction technology is used to adaptively decompose the characteristics according to the signal energy; finally, the transfer-entropy theory and the information-transmission rate are used to determine the vibration-transmission path of the hydropower house. The results show that the main transmission path of the vibration caused by tailwater fluctuation is tailwater pipe (top cover measurement point)→turbine pier (stator foundation measurement point, lower frame foundation measurement point)→generator floor (generator floor measurement point). This research can offer a reference for vibration control and safety monitoring of hydropower houses, and provide a new idea for structural vibration reduction.

Study on the Semiactive Control and Optimal Layout of a Hydropower House Based on Magnetorheological Dampers

With the continuous development of hydropower stations, the capacities and the heads of hydro generator units are increasing, and the plant vibration problem is becoming more and more serious. A numerical simulation method for the vibration reduction control of magnetorheological (MR) dampers suitable for large-scale complex structures was proposed. The method is simple and easy to implement, and the semiactive control of the MR damper could be achieved by adjusting the current switch and size. On the basis of a numerical simulation, a mathematical model for the optimal layout of an MR damper device was established. The objective function was the vertical velocity and the vertical acceleration response of the generator floor. The results showed that the proposed semiactive control numerical simulation method could be applied to the vibration control of the hydropower plant structure, and the vertical velocity and vertical acceleration were reduced by 10.96% and 12.90%, respectively, compared with those without structural vibration control. At the same time, the proposed optimized layout method was effective and feasible, and the damping effect of the MR damper could be effectively improved through the optimized layout.

Research on the Digital Twin Model of Fuchunjiang Hydropower Plant Based on 3D Laser Scanning Technology

With the development and application of 3D laser scanning technology, the efficiency and accuracy of 3D reverse modeling have been greatly improved. In this paper, 3D laser scanning technology is used to establish the 3D model of the hydropower house and main equipments of Fuchunjiang Hydropower Plant, which can truly restore the internal structure and equipments layout of the power station, and solve the difficulties in realizing the digital power station construction due to incomplete or missing drawings of the old power station. The 3D model of the hydropower house and main equipments of Fuchunjiang Hydropower Plant established in this paper not only forms the valuable virtual assets of the power station, but also lays the foundation for flood control emergency plan simulation and 3D maintenance training of the power station, which has a wide field of application with good prospects.

Mathematical modeling and nonlinear vibration analysis of a coupled hydro-generator shaft-foundation system

This paper presents a method to investigate the overall nonlinear dynamics of coupled hydro-generator shaft-foundation system. A novel coupled dynamic mathematical model is developed, which consists of mutual coupled foundation vibrations, external random excitation of foundation, besides classical dynamics of nonlinear hydro-generator shaft system. Previous coupled vibration analysis of water turbine generator unit and foundation (hydropower house) is based on finite element modeling of foundation system. But the too many discrete degrees of freedom in finite element model will result in difficulty of nonlinear dynamic calculation and infeasibility of the vibration controller design. In this study, a simplified equivalent lumped-mass model for foundation system is established using the natural vibration characteristics of hydropower house. The model of foundation random external excitation is proposed and simulated by a combination of bounded noise and harmonics. Then by calculating kinetic energy and potential energy of the coupled hydro-generator shaft-foundation system, a nonlinear dynamic differential equations of the coupled system based on Lagrangian equation are derived. After that Runge-Kutta algorithm is employed for the coupled system's nonlinear responses. The axis orbit diagram, poincaré map and bifurcation diagram are then used to investigate the effect of foundation system and some of the relevant parameters on the transverse vibration of the coupled system. The variable laws and its inner mechanism of the coupled system are revealed further. The advantage of this coupled mathematical model for hydro-generator shaft-foundation system is convenient to capture the key dynamic features of the coupled nonlinear system. The results of all these analyses have enriched the dynamical behaviors of a coupled hydro-generator shaft-foundation system.

Research on coupling vibration of hydropower house

In order to describe and express the hydraulic vibration source as the exciting force in the vibration analysis of hydropower house, a new coupling method for vibration analysis of house structure-flow passage turbulence is proposed in this paper, and then, the finite element coupling model of Xiangjiaba house is developed. Based on the turbulent field and house structure vibration calculated in the time domain, the coupling vibration relationship between hydraulic vibration source and hydropower house is studied. Fluid pressure fluctuations are mainly caused by low frequency vortex in taper pipe of draft tube and Rotor/Stator interaction; both the low frequency vibration displacements on generator floor which are at primary frequency of 0.625 Hz and 1.25 Hz and the low frequency vibration velocities on generator floor which are at primary of 0.626 Hz and 9.375 Hz are caused by low frequency vortex in draft tube. The results show that the coupling method and corresponding finite element model initiated in this paper succeed in solving the description and expression of hydraulic vibration source. Due to short calculation time and inadequate setting of fluid initial condition, the distributions of maximum vibration value need further research.

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.

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.

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.

Sliding Behaviour of Steel Liners on Surrounding Concrete in c-Cross-sections of Spiral Case Structures

A hydropower house substructure, which is also called a spiral case structure (SCS), is usually made of steel-lined concrete. The research to date has tended to focus on the material non-linearity rather than the contact non-linearity in SCSs. The aim of this study is thus to examine the contact friction between the two components of a SCS, namely, the steel liner and the concrete. A structural finite element analysis (FEA) of a SCS was performed using commercial software. The available Coulomb friction model used to describe the contact nonlinearity has been validated based on the well-known push-off tests in 1985. The findings of this study suggest that, under internal water pressure (IWP), the steel liner will significantly slide towards the membrane’s extension range along the internal surface of the surrounding concrete in a c-cross-section of a SCS. Stronger friction leads to more IWP-resisting participation by the surrounding concrete. Based on this understanding, we argue that the friction coefficient should be recognized as an important design parameter. The exterior surface condition of steel spiral cases should be given a greater role in engineering practices of SCSs.

The Dynamic Analysis of Hydropower House and Unit System in Coupled Hydraulic-mechanical-electric Factors

A hydraulic-mechanical-electric and structures coupled model of hydropower station system including subsystem models of the penstock, hydro-turbine model, speed governor, synchronous generator as well as grid, rotor-bearing system and powerhouse structure is established. This model is used to simulate the small fluctuation transient process of 10% load-up in the part load condition for hydropower station. Mechanical eccentric force, unbalanced magnetic pull and vortex pressure fluctuation at inlet of draft tube are considered in the numerical calculation. The interaction between hydraulic-mechanical-electric coupled factors and structural vibration properties during the small fluctuation transient process is studied. The results indicate that the speed regulation for turbine has very litter impact on the transient process of generator. In the process of small fluctuation with loading method in this paper, structure of powerhouse is greatly influenced by vortex pressure pulse in the draft tube, and the vibration of unit is excited by loads which caused by itself rotating.

Control of fault lay-out on seismic design of large underground caverns

Although buried structures are generally believed to suffer a lesser degree of damage in the event of earthquake – than that of over-ground structures – significant damage has been widely reported to buried assets after major earthquakes, including the 1995 Kobe and the 2008 Wen-Chuan. Discontinuity is one key feature of rock as the supporting medium around subsurface excavated spaces. Joints, faults and bedding planes influence, by-and-large, the stability of structures made from/into rock. In particular, fault system around underground caverns such as hydropower house has a marked control on assets’ seismic stability. This study builds on the current understanding through vigorous numerical modelling of fault-structure system under seismic excitation. A parametric approach is followed to determine the most critical layout of a single fault crossing a benchmark cavern. Fault system is systematically broken down into several combinations of dips and intersection points with cavern wall. For each case, a nonlinear dynamic analysis is conducted. To simulate the discontinuous medium, the hybrid finite difference – discrete element code CA2 (Continuum Analysis 2 dimensional) is implemented. The work showed that, similar to static conditions, fault influences the seismic stability of underground caverns through a tendency in extending the plastic zones and increasing displacements as well as asymmetric distribution of the latter and the former in rock medium. A 40–50° dip, single-point-intersection-on-crown k0=1 fault layout renders the most critical combination from both ultimate and serviceability limit states perspective. Under earthquake loading conditions however, the critical limit states condition took place for single fault intersected the cavern at heel and sidewall. The latter critical condition led to the tensile failure of cavern right sidewall. For faults intersecting the carven crown and having a k0=0.5, collapse would be more likely as fault dip increases. Collapse would be less likely with increasing dip for k0=0.5 fault crossing the bed and sidewall of caverns.

Optimal sensor placement in hydropower house based on improved triaxial effective independence method

The capacity and size of hydro-generator units are increasing with the rapid development of hydroelectric enterprises, and the vibration of the powerhouse structure has increasingly become a major problem. Field testing is an important method for research on dynamic identification and vibration mechanisms. Research on optimal sensor placement has become a very important topic due to the need to obtain effective testing information from limited test resources. To overcome inadequacies of the present methods, this paper puts forward the triaxial effective independence driving-point residue (EfI3-DPR3) method for optimal sensor placement. The EfI3-DPR3 method can incorporate both the maximum triaxial modal kinetic energy and linear independence of the triaxial target modes at the selected nodes. It was applied to the optimal placement of triaxial sensors for vibration testing in a hydropower house, and satisfactory results were obtained. This method can provide some guidance for optimal placement of triaxial sensors of underground powerhouses.

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.

Identification of the nonlinear vibration characteristics in hydropower house using transfer entropy

The nonlinear behavior is the primary attribute of the dynamic system stability. In this study, the time-delayed transfer entropy method is proposed to identify the nonlinear dynamic behavior of hydropower house and civil construction, including the transport directionality of information, cracked damage location, and degree of dynamic nonlinearity. Differing from the objects investigated in currently available literature, large-scale civil engineering structures such as hydropower house are more complex and larger size, which stimulate the demand for special identification techniques. Due to the fact that nonlinearity of hydropower house can be induced by many types of interactions between structure and mechanism, a simple similarity model of a multistory building, including damaged contact nonlinearity is studied first following by a discussion of the method for identifying information transmission directionality of the linear or nonlinear structure. The method for identifying the source and degrees of structural nonlinearity vibration is described. Furthermore, the procedure for identification of nonlinearity dynamic behavior in the hydropower house structure based on transfer entropy is studied based on a prototype field experiment under various load cases. Rather than the traditional linear signal processing tools and identification methods, the advantage of this proposed method is to identify the nonlinearity dynamic characteristics of hydropower house structure. This study provides a valuable reference for identifying the damage-induced nonlinearities in civil engineering structures as well as studying the nonlinear dynamic characteristics of hydropower house.

Coupled Vibration Analysis of Water Turbine Generator Unit and Hydropower Station House

The dynamic characteristics of shaft system in water turbine generating set and hydropower house structure is investigated by using the APDL procedure in ANSYS. The coupled vibration model which contains unit piers, hydropower house structure and water turbine generating set is developed. In this model, the nonlinear dynamic characteristics of the supporting structure (radial bearing) in water turbine generating set and the flexibility of unit piers and hydropower house structure are all considered. Through the revolving periodic transient results of the former four generating sets, the dynamic response of the shaft system in water turbine generating set and the dynamic characteristics of the hydropower house structure are analyzed. The interaction between the hydropower house structure and the water turbine generating set is discussed, which provide useful references to anti-vibration design of the hydropower house structure.

Analysis on Vibration Conductivity in Walls of Hydropower House Based on Power Flow Theory

Basing on the theory of power flow, frequency response analysis was acted on in a hydropower house under dominant frequency with measured data of Three Gorges Station in spiral case and draft tube. Power flow in walls was calculated by APDL procedure and the properties were analyzed. The conclusion is that longitudinal wave is the main method in walls of the powerhouse, energy is reflected and stacked at the top of the walls. Displacement along the river changes and power flow in walls decays obviously. Intensity of vibration origin and distance between the vibration and the wall are both the influencing factors，increasing the stiffness of buttressed walls takes the role of limiting flexural wave and shear wave effect

Static and dynamic damage analysis of mass concrete in hydropower house of Three Gorges Project

This paper establishes a 3D numerical model for 15# hydropower house of the Three Gorges Project (TGP) and performs a nonlinear static and dynamic damage analysis. In this numerical model, a coupling model of finite and infinite elements for simulating infinite foundation of hydropower station is adopted. A plastic-damage model based on continuum damage mechanics, which includes the softening and damage behavior under tension is considered for the concrete material. The dynamic equilibrium equations of motion are solved by using the Hilber-Hughes-Taylor (HHT) time integration method. Firstly, the static damage response analysis of the hydropower station is conducted due to high tensile stress resulting from large water head and diameter of an inlet pipe. Then, on the basis of static simulation, the dynamic damage analysis of hydropower house subjected to earthquake motion is simulated. Numerical results show that under large water head and diameter of an inlet pipe of the project, the damages are mainly located near the top of the spiral case from the inlet section to the 0° section; under combined loadings of static loads and earthquake, the damages of the concrete surrounding the spiral case increase insignificantly; however, some damages occur on the side walls of the main powerhouse.

Effect of modeling range on structural analysis for powerhouse of hydroelectric power plant by FEM

In this paper, three different modeling ranges were selected in the structural analysis for a hydropower house. The analysis was carried out using ABAQUS 6.6. The modeling range has a remarkable effect on finite element method (FEM) calculation result at the middle position of typical cross-sections where the concrete is relatively thin, and at the region close to turbine floor. If the ventilation barrel, floor slabs and columns above turbine floor are excluded from FEM model, the maximum rise difference of pedestal structure increases by about 24% compared with that of the whole model. It is indicated that different modeling ranges indeed affect FEM calculation result, and the structure above turbine floor in the FEM model should be included.

Nonlinear dynamic analysis of the Three Gorge Project powerhouse excited by pressure fluctuation

This study established a 3D finite element model for 15# hydropower house of the Three Gorges Project (TGP) and performed a nonlinear dynamic analysis under pressure fluctuation. In this numerical model, the stiffness degradation in tension for concrete was considered on the basis of the continuum isotropic damage theory. Natural vibration frequencies of the damaged and undamaged structures were compared after static water pressure was applied. Then a study was further conducted on forced vibration of the powerhouse with pre-existing damages under pressure fluctuation that acts on the flow passage; displacement, velocity and acceleration of the important structural members were afterwards presented and checked. Numerical results show that tensile damages in concrete surrounding the spiral case only exert significant impact upon the dynamic characteristics of substructure but show little effect on the superstructure. Nevertheless vibrations of the powerhouse are still under the recommended vibration limits.