Runaway Instability of Pump-Turbines in S-Shaped Regions Considering Water Compressibility

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Wei Zeng ◽  
Jiandong Yang ◽  
Wencheng Guo
Keyword(s):  
Elastic Wave ◽  
Stability Criterion ◽  
Simulation Software ◽  
Theoretical Research ◽  
Plant Design ◽  
Stability Criteria ◽  
Pump Turbine ◽  
Characteristic Curves ◽  
Pumped Storage ◽  
The Stability

Pump-turbine characteristics greatly affect the operational stability of pumped-storage plants. In particular, the S-shaped region of the characteristic curves leads to severe instability during runaway conditions with servomotor failure. Thus, this paper aims to investigate the runaway stability criterion by considering all of the important effects in the hydromechanical system. The criterion also helps to judge the S-characteristics of pump-turbines and can provide a guide for plant design and turbine optimization. First, the pump-turbine characteristic curves are locally linearized to obtain formulae for the relative changes of discharge and torque, which depend on the relative changes of rotational speed and water head. Control theory is then applied to analyze the high-order system, by importing the transfer function of the conduits in the elastic mode. Two different kinds of oscillation are found, associated with water inertia and elasticity, based on the established theoretical mathematical model. New stability criteria for the inertia wave in both rigid and elastic modes are developed and compared. The comparison reveals the effect of the water elasticity on runaway instability, which has often been neglected in the previous work. Other effects, such as friction loss and the timescales of water flow and machinery, are also discussed. Furthermore, the elastic wave, which often has a higher frequency than the inertia wave, is also studied. The stability criterion is deduced with analyses of its effects. Based on the stability criteria for the inertia wave and elastic wave, the unstable regions for two waves of the S-shaped curves are plotted. The results are applied to explain the development from inertia wave to elastic wave during transient behavior at runaway conditions. Model tests of runaway conditions were conducted on a model pumped storage station and the experimental data show good agreement with the theoretical analyses regarding the instability of the inertia wave. Further analyses and validations are made based on transient simulations. The simulation software topsys, which uses the method of characteristics (MOC) and a unit boundary represented by a spatial pump-turbine characteristic surface, was applied to analyze the elastic wave. This also supports the conclusions of the theoretical research.

Intrinsic Thermal Stability of Anisotropic Thin-Film Superconductors

1990 ◽  
Vol 112 (1) ◽  
pp. 10-15 ◽  
Author(s):  
M. I. Flik ◽  
C. L. Tien
Keyword(s):  
Thin Film ◽  
Thermal Stability ◽  
Stability Criterion ◽  
High Temperature Superconductors ◽  
Stability Criteria ◽  
Anisotropic Thermal Conductivity ◽  
Operating Current ◽  
Released Energy ◽  
The Stability ◽  
Thermal Stability Of

Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without resistance at all times after the occurrence of a localized release of thermal energy. This novel stability criterion is different from the cryogenic stability criteria for magnets and has particular relevance to thin-film superconductors. Crystals of ceramic high-temperature superconductors are likely to exhibit anisotropic thermal conductivity. The resultant anisotropy of highly oriented films of superconductors greatly influences their thermal stability. This work presents an analysis for the maximum operating current density that ensures intrinsic stability. The stability criterion depends on the amount of released energy, the Biot number, the aspect ratio, and the ratio of the thermal conductivities in the plane of the film and normal to it.

Domain Partitioned Transformation of Pump-Turbine Characteristic Curves in 3-D Space

2014 ◽  
Author(s):  
Wei Zeng ◽  
Jiandong Yang ◽  
Yongguang Cheng
Keyword(s):  
Guide Vane ◽  
Theoretical Method ◽  
Transformation Method ◽  
Measured Data ◽  
Pump Turbine ◽  
Characteristic Curves ◽  
Hydraulic Transient ◽  
Transient Simulations ◽  
Pumped Storage ◽  
Conventional Representation

Pump-turbine characteristic curves are the most important boundary condition in the hydraulic transient simulation of a pumped-storage hydropower station. Conventional representation of them, however, has serious defects, For instance, the “S” and “hump” shapes, composed of multiple values and steep twists, lead to the difficulty in interpolation between known guide-vane opening curves, which is necessary in hydraulic transient simulations. Here, a new transformation method was figured out to settle this problem thoroughly and to improve the accuracy of interpolation between the constant opening curves. Prior to the transformation, the characteristic curves are partitioned into eight domains. Curves of each domain were transformed through different formulae that fit the curves well. Eight characteristic surfaces in the 3-D space can be obtained by adding the guide vane opening as the coordinate axis. The theoretical method has been validated by the excellent agreements achieved by comparing the curves interpolated on the characteristic surfaces with the measured data.

New stability criteria for a class of systems arising in neural network control and fuzzy systems

2000 ◽  
Vol 214 (1) ◽  
pp. 1-8
Author(s):  
Y Fang ◽  
T G Kincaid ◽  
S Li
Keyword(s):  
Neural Network ◽  
Stability Criterion ◽  
Fuzzy Systems ◽  
Neural Control ◽  
Network Control ◽  
Neural Network Control ◽  
Stability Criteria ◽  
Simple Derivation ◽  
The Stability

In this paper, the stability of a class of systems arising from neural control and fuzzy systems is studied. A new unifying stability criterion is presented using a very simple derivation. This result generalizes some previous results; some easily testable conditions are obtained.

scholarly journals Stability Criterion for Mass Oscillation in the Surge Tank of a Hydropower Station Considering Velocity Head and Throttle Loss

Energies ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 5247
Author(s):  
Wei Huang ◽  
Jiming Ma ◽  
Xinlei Guo ◽  
Huokun Li ◽  
Jiazhen Li ◽  
...  
Keyword(s):  
Stability Criterion ◽  
Influencing Factor ◽  
Hydropower Station ◽  
Velocity Head ◽  
Surge Tank ◽  
Critical Stability ◽  
Basic Equations ◽  
Pumped Storage ◽  
The Stability ◽  
Hydropower Stations

Surge tanks (STs) are important facilities for ensuring the safety of hydropower stations. Reducing the ST size under the premise of ensuring stable mass oscillations within the ST is the main issue. First, according to the basic equations of the mass oscillation for a hydropower station with an ST, a novel expression of the critical stability section of an ST is deduced considering the velocity head and throttle loss. Then, the sensitivity of each influencing factor of the proposed stability criterion is analyzed. Ultimately, through the simulation of small oscillation transients in two case studies, the water level oscillations (WLOs) in an ST based on three stability criteria are compared. The results show that a 20% smaller ST in a hydropower station may result in 10.4% larger oscillations and a 60% smaller ST in a pumped storage power station may result in 14.3% larger oscillations. Compared with the Thoma criterion and the Chinese specification criterion, the stability criterion proposed in this paper can safely reduce the size of the ST since it considers the influence of the velocity head and throttle loss. The proposed stability criterion can provide an important reference for the optimal design of the STs.

Construction of Pump-Turbine Characteristics at Any Specific Speed by Domain-Partitioned Transformation

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Wei Zeng ◽  
Jiandong Yang ◽  
Yongguang Cheng
Keyword(s):  
Transformation Method ◽  
Design Stage ◽  
Characteristic Surface ◽  
Pump Turbine ◽  
Characteristic Curves ◽  
Preliminary Design Stage ◽  
Measured Characteristic ◽  
Specific Speed ◽  
Surface Meshes ◽  
Pumped Storage

Pump-turbine characteristics are important for designing pumped-storage plants and indispensable for simulating hydraulic transients, but are often not available in the preliminary design stage. Therefore, constructing a set of pump-turbine characteristics is necessary, when no suitable characteristics at the same specific speed can be used for substitution. In this paper, we propose a new method for pump-turbine characterization at any specific speed using a database of 25 available sets of pump-turbine characteristics. The intersecting curves, defined by the intersections of the characteristic curves with a coordinate axis, are formularized to prepare for the characterization primarily. Next is an introduction of a transformation method for characteristic curves base on domain partition, through which the curves are transformed into eight characteristic surface meshes in eight separate domains. Then, we present the construction procedures in each domain, which include merging the transformed surface meshes for all the sets of collected characteristic curves into a cube mesh, constructing a super surface by interpolation to construct the regular characteristic surface meshes for an arbitrary specific speed, and transforming the constructed meshes reversely to get the conventional characteristic curves. This method is verified by comparing them to measured characteristic curves with reasonable accuracies.

scholarly journals Stability Criterion for Dynamic Gaits of Quadruped Robot

2018 ◽  
Vol 8 (12) ◽  
pp. 2381 ◽  
Author(s):  
Yan Jia ◽  
Xiao Luo ◽  
Baoling Han ◽  
Guanhao Liang ◽  
Jiaheng Zhao ◽  
...  
Keyword(s):  
Dynamic Stability ◽  
Stability Criterion ◽  
Quadruped Robot ◽  
Stability Criteria ◽  
Irregular Terrain ◽  
Quadruped Robots ◽  
Simulation Results ◽  
Zero Moment ◽  
The Stability ◽  
Dynamic Gait

Dynamic-stability criteria are crucial for robot’s motion planning and balance recovery. Nevertheless, few studies focus on the motion stability of quadruped robots with dynamic gait, none of which have accurately evaluated the robots’ stability. To fill the gaps in this field, this paper presents a new stability criterion for the motion of quadruped robots with dynamic gaits running over irregular terrain. The traditional zero-moment point (ZMP) is improved to analyze the motion on irregular terrain precisely for dynamic gaits. A dynamic-stability criterion and measurement are proposed to determine the stability state of the robot and to evaluate its stability. The simulation results show the limitations of the existing stability criteria for dynamic gaits and indicate that the criterion proposed in this paper can accurately and efficiently evaluate the stability of a quadruped robot using such gaits.

Completeness on the stability criterion of fractional order LTI systems

2017 ◽  
Vol 20 (1) ◽  
Author(s):  
Yiheng Wei ◽  
Yuquan Chen ◽  
Songsong Cheng ◽  
Yong Wang
Keyword(s):  
Fractional Order ◽  
Stability Criterion ◽  
Positive Definite Matrix ◽  
Order System ◽  
Linear Matrix ◽  
Matrix Inequalities ◽  
Stability Criteria ◽  
The Stability ◽  
Definition Of ◽  
And Control

AbstractThe importance of the concept of stability in fractional order system and control has been recognized for some time now. Recently, it has become evident that many conclusions were drawn, but little consensus was reached. Consequently, there is an urgent need for a much deeper understanding of such a concept. With the definition of fractional order positive definite matrix, a set of equivalent and elegant stability criteria are developed via revisiting a stability criterion we proposed before. All the results are formed in terms of linear matrix inequalities. Afterwards, a series of interesting properties of these criteria are revealed profoundly, including completeness, singularity, conservatism, etc. Eventually, a simulation study is provided to validate the effectiveness of the obtained results.

scholarly journals Study on instability failure mode and monitoring early warning standard of surrounding rock in fully weathered argillaceous sandstone section of large section tunnel

2019 ◽  
Vol 136 ◽  
pp. 04023
Author(s):  
Ming Zhao ◽  
Ke Li ◽  
Hong Yan Guo ◽  
KaiCheng Hua
Keyword(s):  
Limit State ◽  
Stable State ◽  
Simulation Software ◽  
Surrounding Rock ◽  
Large Section ◽  
Rock Stability ◽  
Geological Conditions ◽  
Construction Step ◽  
The Face ◽  
The Stability

Based on the special geological conditions of a tunnel in Qingyuan section of Huizhou-Zhanzhou Expressway, FLAC3d numerical simulation software is used to simulate the rheological properties and instability of surrounding rock in large-section fully weathered sandstone section, and the stability and loss of surrounding rock are analyzed. The deformation of the dome and the face at steady state is analyzed. It is found that: 1) when the surrounding rock is in a stable state, the deformation curve of the dome is smooth. When the surrounding rock of the face is unstable, the front of the face appears ahead. Deformation should be first strengthened on the surrounding rock in front of the face. 2) The arched foot is an important part of the instability of the surrounding rock. In order to prevent the expansion of the collapsed part, the arched part should be reinforced. 3) In order to obtain the limit state of surrounding rock stability, the strength of surrounding rock is reduced, and the strength reduction coefficient corresponding to the displacement sudden point is taken as the safety factor of rock stability around the hole, and the stability safety coefficients of surrounding rock of each construction step are greater than 1.2. 4) The dynamic standard values of deformation control in the whole construction stage are obtained by analyzing the deformation curves of each data monitoring point with time in the corresponding time period of each construction step.

Dissipative instability of the MHD tangential discontinuity in magnetized plasmas with anisotropic viscosity and thermal conductivity

1996 ◽  
Vol 56 (2) ◽  
pp. 285-306 ◽  
Author(s):  
M. S. Ruderman ◽  
E. Verwichte ◽  
R. Erdélyi ◽  
M. Goossens
Keyword(s):  
Thermal Conductivity ◽  
Dispersion Equation ◽  
Viscosity Coefficient ◽  
Tangential Discontinuity ◽  
Stability Criteria ◽  
Threshold Velocity ◽  
Cold Plasmas ◽  
The Difference ◽  
The Stability ◽  
Anisotropic Viscosity

The stability of the MHD tangential discontinuity is studied in compressible plasmas in the presence of anisotropic viscosity and thermal conductivity. The general dispersion equation is derived, and solutions to this dispersion equation and stability criteria are obtained for the limiting cases of incompressible and cold plasmas. In these two limiting cases the effect of thermal conductivity vanishes, and the solutions are only influenced by viscosity. The stability criteria for viscous plasmas are compared with those for ideal plasmas, where stability is determined by the Kelvin—Helmholtz velocity VKH as a threshold for the difference in the equilibrium velocities. Viscosity turns out to have a destabilizing influence when the viscosity coefficient takes different values at the two sides of the discontinuity. Viscosity lowers the threshold velocity V below the ideal Kelvin—Helmholtz velocity VKH, so that there is a range of velocities between V and VKH where the overstability is of a dissipative nature.

The flow of a micropolar liquid layer down an inclined plane

1968 ◽  
Vol 64 (2) ◽  
pp. 513-526 ◽  
Author(s):  
A. J. Willson
Keyword(s):  
Thin Films ◽  
Steady State ◽  
Liquid Layer ◽  
Stability Criterion ◽  
Long Waves ◽  
Inclined Plane ◽  
The Stability ◽  
Micropolar Liquid

AbstractConsideration is given to the flow of a micropolar liquid down an inclined plane. The steady state is analysed and Yih's technique is employed in an investigation of the stability of this flow with respect to long waves. Detailed calculations are given for thin films and it is shown that the micropolar properties of the liquid play an important role in the stability criterion.

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