A Study of the Effect of Mixed Cores on the Stability of BWRs

2010 ◽  
Author(s):  
Jose March-Leuba ◽  
Weidong Wang ◽  
Tai L. Huang
Keyword(s):  
Pressure Drop ◽  
Natural Circulation ◽  
Strong Dependence ◽  
Stability Margin ◽  
Fuel Type ◽  
Stability Margins ◽  
Full Power ◽  
Set Up ◽  
The Stability ◽  
Fuel Elements

Cores loaded with a mixture of fuel types are known to reduce stability margins. Mixed fuel cores have become more common as utilities change fuel suppliers, or when fuel vendors upgrade their fuel designs to take advantage of improved thermal and mechanical margins. This paper studies some of the physical processes that reduce the stability of mixed cores. A number of runs have been performed using the LAPUR6 stability code to evaluate the effect on mixed cores on the stability of a typical BWR. To this end, two fuel types have been set up with two different single-phase to two-phase pressure drop ratios by artificially adjusting the spacer and inlet orifice friction coefficients. The flow and pressure drop characteristics of both fuels have been matched at full flow, full power conditions. All manufacturers match the pressure drop of new fuels so that the flow distributions among the new and old fuel elements operating at the same power are approximately constant. The critical power ratio and thermo-mechanical criteria are typically limiting at full power; therefore matching the flow performance at full power maximizes the margin to these criteria. Stability is of concern at low flows, especially at natural circulation, where the thermal-hydraulic conditions are significantly different from full flow and power. Our simulations show that even if two fuel elements are perfectly matched at full flow, the axial void fraction distribution changes significantly when the flow is reduced to natural circulation conditions and the two fuel elements are not fully thermal-hydraulically compatible at the reduced flows. Basically, the two fuel types set up two separate natural circulation lines, and one of the fuel types essentially starves the other from flow. Since stability has such a strong dependence with channel flow, the reactor stability is controlled by the fuel type that has the smaller flow at natural circulation. A counterintuitive result of this study shows that, in general, loading a more stable fuel type into a mixed core has the opposite effect, and the stability margin of that mixed core is lower until the new, more stable fuel becomes dominant. Because of the burnable Gadolinium in most modern BWR fuels, the highest reactivity fuel elements are the once-burned. Loading a more stable fuel type starves the flow of the high-reactivity older fuel, reducing the stability margin.

Model Reduction of a Parametrically Excited Drivetrain

2012 ◽  
Author(s):  
Thomas Pumhoessel ◽  
Peter Hehenberger ◽  
Klaus Zeman
Keyword(s):  
Stability Margin ◽  
Original System ◽  
Reduced Model ◽  
Parametrically Excited ◽  
System Parameters ◽  
Additional Stability ◽  
System Equations ◽  
The Difference ◽  
Set Up ◽  
The Stability

The complexity of engineering systems is continuously increasing, resulting in mathematical models that become more and more computationally expensive. Furthermore, in model based design, for example, system parameters are subject of change, and therefore, the system equations have to be evaluated repeatedly. Hence, there is a need for providing reduced models which are as compact as possible, but still reflect the properties of the original model in a satisfactory manner. In this contribution, the reduction of differential equations with time-periodic coefficients, termed as parametrically excited systems, is investigated using the method of Proper Orthogonal Decomposition (POD). A reduced model is set up based on the solution of the original system for a certain parametric combination resonance of the difference type, resulting in an additional stability margin of the trivial solution. It is shown that the POD reduced model approximates the stability behavior of the original system much better than a modally reduced model even if system parameters are subject of change.

scholarly journals Comparative Study of Control Strategies for Stabilization and Performance Improvement of DC Microgrids with a CPL Connected

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2663
Author(s):  
Isaías V. de Bessa ◽  
Renan L. P. de Medeiros ◽  
Iury Bessa ◽  
Florindo A. C. Ayres Junior ◽  
Alessandra R. de Menezes ◽  
...  
Keyword(s):  
Control Strategies ◽  
Output Feedback Control ◽  
Stability Margin ◽  
Performance Indices ◽  
Dc Microgrid ◽  
Stability Margins ◽  
Dc Microgrids ◽  
Constant Power Loads ◽  
And Performance ◽  
The Stability

The DC microgrid system is composed by converters that operate like feeders and loads. Among these loads, we highlight the constant power loads (CPLs) that may cause instability in the microgrid, observed in the form of undesired oscillations due to its negative impedance behavior. Therefore, this work proposes to use performance indices and stability margins to evaluate state and output feedback control strategies for stabilization of DC microgrids. In particular, it is proposed to evaluate the stability margin of the proposed methodologies by means of the impedance relations in the microgrid based on the Middlebrook criterion. Our simulations and tests showed the relation between the performance and stability degradation and the microgrid impedances variation.

Study of Casing Treatment Effects in Axial Flow Compressors

1975 ◽  
Vol 97 (4) ◽  
pp. 477-483 ◽  
Author(s):  
M. P. Boyce ◽  
R. N. Schiller ◽  
A. R. Desai
Keyword(s):  
Axial Flow ◽  
Stability Margin ◽  
Stable Operation ◽  
Stability Margins ◽  
Casing Treatment ◽  
Blade Tip ◽  
Flow Compressor ◽  
The Stability ◽  
Casing Treatments ◽  
Axial Flow Compressors

The phenomenon of surge in an axial flow compressor has long eluded the analytical fluid dynamist. In the recent years, a growing degree of improvement and sophistication in the design of axial flow compressors to achieve higher pressure ratios has resulted in increasingly narrow domains of stable operation. A search for improving stability margins revealed the importance of the blade tip region and casing treatments. The authors have approached the problem by both experimental and analytical methods. The results are mutually confirming. Important new inroads have been made in understanding the flow in the blade tip region, operation of casing treatments and the mechanism of the onset of surge. Some significant conclusions in the selection and design of casing treatments and their effects on the stability margin are presented and explained on the basis of experimental and theoretical results.

Stabilization of a Translating Tensioned Beam Through a Pointwise Control Force

1998 ◽  
Vol 122 (2) ◽  
pp. 322-331 ◽  
Author(s):  
W. D. Zhu ◽  
B. Z. Guo ◽  
C. D. Mote,
Keyword(s):  
Stability Margin ◽  
Numerical Approach ◽  
Distributed Model ◽  
Control Force ◽  
Stability Margins ◽  
Distribution Of Eigenvalues ◽  
Modes Of Vibration ◽  
The Subject ◽  
The Stability ◽  
Necessary And Sufficient

A spectral analysis determining asymptotically the distribution of eigenvalues of a constrained, translating, tensioned beam in closed form is the subject of this paper. The constraint is modeled by a spring-mass-dashpot subsystem that is located at any position within the span of the beam. It can represent a feedback controller with a collocated sensor and actuator. The necessary and sufficient condition that ensures a uniform stability margin for all the modes of vibration is determined. Influences of system parameters on the distribution of eigenvalues are identified. The analytical predictions are validated by numerical analyses. The constraint location maximizing the stability margin of the distributed model is predicted through a combined analytical and numerical approach. The implications and utility of the results are illustrated. The methodology developed can be extended to predict stability margins and optimize control parameters for controlled translating beams with other types of boundary conditions and controller structures. [S0022-0434(00)00702-4]

Stability Measures and Criteria for Autonomous Mobile Robotic Platforms: Analysis, Comparison and Numerical Evaluation

2019 ◽  
Author(s):  
Kaveh Nazem Tahmasebi ◽  
Roberto Belotti ◽  
Renato Vidoni ◽  
Karl Von Ellenrieder
Keyword(s):  
Mobile Robot ◽  
Center Of Mass ◽  
Stability Margin ◽  
Base Surface ◽  
Point Energy ◽  
Stability Margins ◽  
Stability Measure ◽  
Mass Moment ◽  
Angle Stability ◽  
The Stability

Abstract The tip-over instability of an autonomous mobile robot is a significant problem as it can diminish its maneuverability and increase the possibility of damaging the robot and its surrounding environment. For these reasons, it is important to define the stability margin and predict the edge of the tip-over instability considering different robot specifications and environmental conditions. Different stability measures have been developed to evaluate and analyze robot stability margins for diverse conditions. In this work, the Zero Moment Point, Energy Stability Margin, Force-Angle Stability Measure, and Mass-Moment Height Stability Measure methods are considered and applied to different mobile robot architectures including three-wheeled, four-wheeled (with rectangular and trapezoidal base surface) and articulated systems. The stability margins are discussed considering the four different stability criteria and evaluating the effect of a sloped surface. Then, the sensitivity of the tip-over instability in relation to the variation of the center of mass height as an important robot configuration parameter is evaluated. Finally, after a theoretical extension of the Force-Angle Stability and Mass-Moment Height stability measurement methods, the articulated mobile robot’s stability margin is considered and evaluated.

Stability margin for robust walking gaits constructed by center of pressure

2016 ◽  
Vol 32 ◽  
Author(s):  
Kuo-Yang Tu ◽  
Cheng-Hsiung Huang ◽  
Jacky Baltes
Keyword(s):  
Center Of Pressure ◽  
Stability Margin ◽  
Humanoid Robots ◽  
Measuring System ◽  
Gait Stability ◽  
Stability Margins ◽  
Double Support ◽  
Walking Gait ◽  
The Stability ◽  
The Mathematical Model

AbstractUsually, humanoid walking gaits are only roughly distinguished between stable and unstable. The evaluation of a stable humanoid walking gait is difficult to quantify in scales. And, it is extremely hard to adjust humanoid robots in suitable a walking gait for different movement objectives such as fast walking, uneven floor walking, and so on. This paper proposes a stability margin constructed by center of pressure (COP) to evaluate the gait stability of humanoid walking. The stability margin is modeled by the COP regions that a humanoid robot needs for stable standing. We derive the mathematical model for COP position by dividing the walking gait into single and double support phases in order to measure the stability of the COP regions. An actual measuring system for the stable COP regions is designed and implemented. The measured COP trajectory of a walking gait is eventually evaluated with respect to the stable COP regions for the stability margins. The evaluation focuses on weak stability areas to be improved for robust walking gaits. To demonstrate the robustness of the improved walking gait, we replicate the experiment on three different terrains. The experiments demonstrate that the walking gaits developed based on stable COP region can be applied for different movement objectives.

Numerical Investigation on Transverse Maneuverability of a Vectored Underwater Vehicle Without Appendage

2016 ◽  
Vol 28 (3) ◽  
pp. 371-377 ◽  
Author(s):  
Rongmin Zhang ◽  
◽  
Yuan Chen ◽  
Jun Gao
Keyword(s):  
Kinematic Model ◽  
Stability Margin ◽  
Underwater Vehicle ◽  
Euler Method ◽  
Nonlinear Dynamic Model ◽  
Research Attention ◽  
Spherical Parallel Mechanism ◽  
Six Dof ◽  
Set Up ◽  
The Stability

[abstFig src='/00280003/13.jpg' width=""300"" text='Solid model of a vectored underwater vehicle' ] Vectored underwater vehicles (VUVs) are receiving increasing research attention, in part for their maneuverability. In our work, we apply a novel vectored thruster based on a spherical parallel mechanism to an underwater vehicle. We present and calculate the scaling factor based on the vectored thruster’s configuration parameters and set up a six DOF kinematic model. We construct a nonlinear dynamic model of the VUV without appendages using the Newton-Euler method. To demonstrate the VUV’s transverse maneuverability, we set up a perturbation model in a complex domain using Laplacian transformation, and propose the stability margin of vectored propulsion as a maneuverability index. Many numerical examples are provided to verify the maneuverability of the VUV.

scholarly journals Stability-Guaranteed and High Terrain Adaptability Static Gait for Quadruped Robots

Sensors ◽  
2020 ◽  
Vol 20 (17) ◽  
pp. 4911
Author(s):  
Qian Hao ◽  
Zhaoba Wang ◽  
Junzheng Wang ◽  
Guangrong Chen
Keyword(s):  
Impedance Control ◽  
Stability Margin ◽  
Planning Method ◽  
Legged Robots ◽  
Gait Planning ◽  
Quadruped Locomotion ◽  
Quadruped Robots ◽  
Adjustment Strategy ◽  
Compliant Behavior ◽  
The Stability

Stability is a prerequisite for legged robots to execute tasks and traverse rough terrains. To guarantee the stability of quadruped locomotion and improve the terrain adaptability of quadruped robots, a stability-guaranteed and high terrain adaptability static gait for quadruped robots is addressed. Firstly, three chosen stability-guaranteed static gaits: intermittent gait 1&2 and coordinated gait are investigated. In addition, then the static gait: intermittent gait 1, which is with the biggest stability margin, is chosen to do a further research about quadruped robots walking on rough terrains. Secondly, a position/force based impedance control is employed to achieve a compliant behavior of quadruped robots on rough terrains. Thirdly, an exploratory gait planning method on uneven terrains with touch sensing and an attitude-position adjustment strategy with terrain estimation are proposed to improve the terrain adaptability of quadruped robots. Finally, the proposed methods are validated by simulations.

Study on the characteristics of secondary arc current of UHV high compensation degree TCSC line under the fine-tuning mode

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Baina He ◽  
Yadi Xie ◽  
Jingru Zhang ◽  
Nirmal-Kumar C. Nair ◽  
Xingmin He ◽  
...  
Keyword(s):  
Transmission Line ◽  
Transmission Lines ◽  
Stability Margin ◽  
Transmission Capacity ◽  
Fine Tuning ◽  
Series Compensation ◽  
Arc Current ◽  
Compensation Device ◽  
The Stability ◽  
Recovery Voltage

Abstract In the transmission line, the series compensation device is often used to improve the transmission capacity. However, when the fixed series capacitor (FSC) is used in high compensation series compensation device, the stability margin cannot meet the requirements. Therefore, thyristor controlled series compensator (TCSC) is often installed in transmission lines to improve the transmission capacity of the line and the stability of the system. For cost considerations, the hybrid compensation mode of FSC and TCSC is often adopted. However, when a single-phase grounding fault occurs in a transmission line with increased series compensation degree, the unreasonable distribution of FSC and TCSC will lead to the excessive amplitude of secondary arc current, which is not conducive to rapid arc extinguishing. To solve this problem, this paper is based on 1000 kV Changzhi-Nanyang-Jingmen UHV series compensation transmission system, using PSCAD simulation program to established UHV series compensation simulation model, The variation law of secondary arc current and recovery voltage during operation in fine tuning mode after adding TCSC to UHV transmission line is analyzed, and the effect of increasing series compensation degree on secondary arc current and recovery voltage characteristics is studied. And analyze the secondary arc current and recovery voltage when using different FSC and TCSC series compensation degree schemes, and get the most reasonable series compensation configuration scheme. The results show that TCSC compensation is more beneficial to arc extinguishing under the same series compensation. Compared with several series compensation schemes, it is found that with the increase of the proportion of TCSC, the amplitude of secondary arc current and recovery voltage vary greatly. Considering various factors, the scheme that is more conducive to accelerating arc extinguishing is chosen.

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