Stability Analysis Method Research Articles

System wide‐band oscillation analysis of fractional frequency offshore wind power systems

AbstractThe fractional frequency offshore wind power system (FFOWPS) is a core technology for the long‐distance transmission and integration of the large‐scale offshore wind power. However, the risk of wide‐band oscillation in the FFOWPS has become increasingly prominent due to the inevitable presence of the power electronic devices. The traditional admittance of the frequency converter, which is a crucial component in the FFOWPS, may contain right‐half‐plane (RHP) poles when operating under various control modes. To address this deficiency, this paper establishes a four‐port small‐signal admittance model of a back‐to‐back frequency converter and demonstrates its interconvertibility with the traditional model. On this basis, the wide‐band oscillation analysis method for the FFOWPS is proposed, which explicitly describes the influence of the industrial frequency system, the fractional frequency system, and their coupling interactions on system stability. Simulation results in MATLAB/Simulink verify the proposed stability analysis method, highlight stability misjudgements associated with the traditional admittance, and analyse the impact of the coupling terms on system stability.

Instability of bubbly jets subjected to unrelaxed axial elastic tension

Injection of bubbly jets is a critical process in various fields, such as fuel atomization and petrochemicals. However, existing instability models for bubbly jets have predominantly focused on density variations due to bubble compressibility, largely neglecting the impact of bubbles on the macroscopic rheological properties of the mixture. In this study, we have integrated compressibility with non-Newtonian properties induced by bubbles to explore the evaluation of jet perturbations. Additionally, considering bubble pre-deformation before injection, we particularly examine the role of unrelaxed axial elastic tension in the bubbly jets. Both linear stability analysis and energy budget methods are used to illustrate the contributions of viscosity, elasticity, and compressibility. The results indicate that the viscoelastic effects induced by bubbles can significantly outweigh the effects of compressibility during the jet destabilization process. Notably, a slight unrelaxed tension can markedly increase both the perturbation growth rate and the cutoff wavenumber, potentially making it a more dominant driver of jet instability than the classical surface tension.

Numerical stability analysis of shock-capturing methods for strong shocks II: high-order finite-volume schemes

The shock instability problem commonly arises in flow simulations involving strong shocks, particularly when employing high-order shock-capturing schemes, limiting their application in hypersonic flow simulations. In the current study, the shock instability problem of the fifth-order finite-volume WENO scheme is investigated. To this end, the matrix stability analysis method for the fifth-order scheme is established. Such an analysis method is capable of providing quantitative insights into the stability of shock-capturing and helping elucidate the mechanism causing shock instabilities. Results from the stability analysis and numerical experiments reveal that even dissipative solvers, which are generally believed to be capable of capturing strong shocks stably, also suffer from the shock instability problem when the spatial accuracy is increased to the fifth-order. Further investigation indicates that this is because the quadratic polynomial degenerated from the WENO reconstruction is not applicable for reconstructing variables on the faces near the numerical shock structure. Moreover, the shock instability problem of the fifth-order scheme is demonstrated to be a multidimensional coupled problem. To capture strong shocks stably, it is necessary to have sufficient dissipation on both transverse faces and normal faces in the vicinity of strong shocks. The spatial location of the perturbation leading to instability is also clarified by the proposed matrix analysis and numerical experiments, revealing that the instability arises from the numerical shock structure for the fifth-order scheme. Additionally, the local characteristic decomposition is demonstrated to be helpful to mitigate shock instabilities in high-order cases. Based on these conclusions and the core idea of the MR-WENO scheme, a shock-stable high-order scheme, the MR-WENO-SD scheme, is proposed. Equipped with the hybrid HLLC/HLL solver, this scheme is capable of capturing strong shocks stably while maintaining high-order accuracy. A series of numerical experiments demonstrate its stability and resolution capabilities.

An Investigation of Parameter Sensitivity and a Dynamic Analysis of Subsurface Storage Chambers Utilizing the Finite Difference Method

Underground compressed air energy storage chambers are a promising emerging energy storage technology with strict limitations relating to the stability of the surrounding rock. This study conducted displacement and plastic zone analyses during the excavation and stabilization phases of the chamber utilizing the finite difference method based on engineering data, demonstrating that the stability of salt rock can effectively withstand internal pressures ranging from 0 to 9 MPa, with an average of 15 mm in the Z-axis and 19.23 mm in the X-axis. To further investigate the feasibility of subterranean energy storage reservoirs, the FOS for various surrounding rocks was calculated at different burial depths. These results facilitated a parameter sensitivity analysis on the stability of the surrounding rock of the underground energy storage reservoir. The dynamic reaction of the underground chamber was studied using synthetic seismic wave technology, demonstrating that the seismic capacity of the structure adhered to the code, and the post-seismic displacement remained within the safe range (Z-axis 34 mm, horizontal 19 mm). The results demonstrate the stability analysis method of the chamber and establish a foundation for the extensive implementation of CAES which will contribute to the development of energy storage technology.

Transient Stability-Based Fast Power System Contingency Screening and Ranking

Today’s power systems are operated closer to their stability limits due to the continuously growing load demands, interface to open markets, and integration of more renewable energies. In order to provide operators with clear insight on the current system situation, near real-time power systems dynamic security assessment tools are required. One of the core elements of near real-time dynamic security assessment tools is contingency screening and ranking. Most of the commercially available tools screen and rank contingencies by using the traditional numerical integration or Transient Energy Functions (TEFs) or hybrid methods. The traditional numerical integration method is accurate but computationally intensive and has a slow assessment speed which makes it difficult to identify any insecure contingency before it happens. Despite the TEF method of transient stability analysis being relatively fast, it develops less accurate results due to models simplification and assumptions. This paper introduces transient stability based on fast and robust contingency screening and ranking using an Adaptive step-size Differential Transformation (AsDTM) method. Based on the most current snapshot from Supervisory Control and Data Accusation (SCADA) data, the proposed method triggers AsDTM-based transient stability simulation for each credible contingency and evaluates Transient Stability Indices (TSI) as the normalized weighted sum of squares of errors derived from state variables and complex bus voltages at every simulation time step. Finally, contingencies are ranked based on these TSI and the worst contingency is identified for the next detail assessment. The method is tested on IEEE 9 bus and 39 bus test systems. Test results reveal that the proposed method is faster, robust, and can be used in near real-time dynamic security assessment sessions.

Stochastic stability analysis method for doubly fed generator sets considering random blade stress

AbstractWith the increasing capacity of doubly fed induction generators (DFIGs), the diameter of the wind turbine is increasing, the blades are getting longer and longer, and in the process of power generation, the tower shadow effect as well as the role of wind shear are more obvious, and the random blade stresses caused by this is also getting bigger. Random blade stresses cause random and cyclic fluctuations in the power generated by the wind turbine, and power fluctuations often cause voltage flicker, which affects the control system and power quality. To address the impact of random blade stresses on the grid‐connected stability of DFIG, the results of the traditional stability analysis methods may be too conservative or lead to too high a dimensionality to be analyzed. To solve the above problems, this paper proposes a grid‐connected stochastic stability analysis method for DFIG sets considering random blade stresses based on the stochastic averaging method under the Hamiltonian system. a stochastic dynamics model of the doubly fed wind farm was established by considering random blade stress. Subsequently, using the proposed generalized Hamiltonian principle, the model and energy functions in the proposed Hamiltonian form H, based on the stochastic averaging method (SAM), were established to obtain the system energy diffusion equation. Probability density function and regional stability probability were obtained from explicit expressions of the mean and regression square root processes. The drift and diffusion coefficients were obtained using the SAM, and the backward Kolmogorov equation was derived from the Ito equation to obtain the conditional reliability function and the probability density of the first crossing time. Finally, the effects of torque fluctuations with different stochastic intensities on the grid‐connected stability of doubly fed wind farms were investigated, and the effectiveness of the proposed generalized Hamiltonian SAM applied to the stochastic stability analysis of DFIG was verified by numerical analysis and Monte Carlo simulation. This provides a theoretical foundation for analyzing the grid‐connected stability of DFIG affected by random blade stresses.

Imprints of the Einasto density profile and complexity factor on traversable wormholes in f(R, T) theory

The focus of this work is centered on determining whether traversable wormholes admitting Einasto density profile exist within the framework of f(R, T) gravity. Using the Morris–Thorne spacetime, we express the wormhole configuration and formulate the anisotropic gravitational equations for a particular linear modified model. Afterwards, by considering two different (constant and variable) redshift functions, we derive the shape function for wormholes and examine its potential stability. The developed functions conform to the necessary conditions and form a connection between two spacetime regions that are asymptotically flat. We also examine the viability of resulting wormhole solutions by verifying their violation with the null energy conditions. We also investigate the active gravitational mass and the complexity factor for our solutions. The later quantity is found to be negative near the wormhole throat and becomes zero when moving away from this point. Further, various methods of stability analysis are utilized to assess the developed models. Our results suggest that the constructed wormhole geometries meet the necessary conditions, thereby existing within the considered modified gravity.

Delay-tolerant hierarchical distributed control for DC microgrid clusters considering microgrid autonomy

A microgrid cluster (MGC) is formed by interconnected geographically adjacent microgrids (MGs), which can effectively improve power supply reliability. To fulfill the requirements of coordination between MGs while exerting the autonomy ability of each MG, this paper proposes a hierarchical distributed control method for DC MGCs with MG autonomous-cooperative mode switching. The proposed method can not only realize the proportional current sharing between the MGs and the voltage regulation of the common bus but also allow MGs to operate in autonomous or cooperative mode by establishing and disconnecting the inter-MG communication links. In addition, considering that the delay of inter-MG communication links affects multiple control links of the proposed control method, a delay-dependent stability analysis method based on Padé approximation and eigenvalue spectrum comparison is proposed. By stability analysis, the time delay margin (TDM) is determined, and the key link that determines the TDM is identified as the observer based on the proportional-integral (PI) consensus algorithm. On this basis, the scattering transformation (ST) is introduced to improve the stability of the observer under delay and thus enhance the TDM of DC MGCs, which is confirmed by stability analysis based on a new system model integrating node variables and edge variables. Finally, the performance of the proposed control method and stability analysis results are verified by hardware-in-loop (HIL) tests and MATLAB/Simulink simulations

A Fast Chebyshev Collocation Method for Stability Analysis of a Robotic Machining System with Time Delay

A Fast Chebyshev Collocation Method for Stability Analysis of a Robotic Machining System with Time Delay

Slope stability analysis of unsaturated colluvial slopes based on case studies of rainfall-induced landslides

Landslides in colluvial soils under rainfall have been identified as a significant problem due to their loose, heterogeneous nature and low shear strength. Evaluation of the stability of colluvial slopes under rainfall conditions is challenging. This study investigated two landslide failure case studies of colluvial soils to understand the failure patterns using finite element (FE) and limit equilibrium (LE) slope stability analysis methods under unsaturated conditions. Transient seepage conditions due to rainfall infiltration and failure were analysed using hydromechanical models. Here, a FE fully coupled hydromechanical model and a sequential coupling of a FE hydrological and LE mechanical model were used to evaluate the failure of variably saturated slopes. Results from the case studies revealed that the failure occurred due to the rise in the groundwater table in both cases. It was evident that there can be significant disparities in the pore water pressure profiles with the fully coupled and sequentially coupled analysis. The dynamic capability of the two models can also affect the interplay between the hydrological and mechanical aspects. When the thickness of the colluvium layer is large, the failure could potentially occur as a deep-seated failure along the boundary of overburden and the bedrock surface due to the large driving force. However, when the thickness is small, failure can occur along the colluvium-weathered rock surface. The outcomes from the study will contribute to mitigate the uncertainty of failure prediction of landslides in colluvial soils.

Enhancing slope stability prediction through integrated PCA-SSA-SVM modeling: a case study of LongLian expressway

China is one of the regions most frequently affected by landslides, which have significant socio-economic impacts. Traditional slope stability analysis methods, such as the limit equilibrium method, limit analysis method, and finite element method, often face limitations due to computational complexity and the need for extensive soil property data. This study proposes a novel approach that combines Principal Component Analysis (PCA), Sparrow Search Algorithm (SSA), and Support Vector Machine (SVM) to improve the accuracy of slope stability prediction. PCA effectively reduces data dimensionality while retaining critical information. SSA optimizes SVM parameters, addressing the limitations of traditional optimization methods. The integrated PCA-SSA-SVM model was applied to a dataset of 257 slope stability samples and validated using five-fold cross-validation to ensure the model’s generalization capability. The results show that the model exhibits superior performance in prediction accuracy, precision, recall, and F1-score, with the test set achieving an accuracy of 84.6%, a recall of 84.7%, a precision of 83.1%, and an F1-score of 84.6%. The model’s robustness was further validated using slope data from the LongLian Expressway, demonstrating high consistency with the actual stability status. These findings indicate that the PCA-SSA-SVM-based slope stability prediction model has significant potential for practical engineering applications, providing a reliable and efficient tool for slope stability forecasting. Classify the training samples through cross-validation, using the accuracy of cross-validation as the fitness of the sparrow individual. Retain the optimal fitness value and position information.

Integrated Control of Intelligent Vehicle Driving Stability Using Three-Dimensional Phase Space

<div>To enhance vehicle dynamic stability during driving, we developed a three-dimensional phase space model that incorporates the sideslip angle of center of mass, yaw rate, and lateral load transfer rate. This model enabled real-time evaluation and active control of vehicle stability. First, longitudinal and lateral controllers were implemented to ensure precise vehicle trajectory. Second, a hierarchical control strategy was designed to actively manage the desired sideslip angle, yaw rate, and roll angle based on the vehicle’s destabilizing conditions, thereby maintaining the vehicle within a stable state space. We simulated and tested the stability analysis methods and integrated control strategies for both cars and trucks under DLC (double lane change) and CDC (circular driving condition) scenarios using joint simulations with CarSim/TruckSim and Simulink. The proposed integrated stability control strategy, which combined MPC-based trajectory tracking with direct yaw moment control and active suspension control, enhanced the vehicle’s directional and roll stability. This approach effectively mitigated vehicle instability under extreme conditions. Compared to the MPC lateral tracking control system, the performance of the integrated control system was significantly improved. In the DLC scenario, the maximum values of the sedan’s lateral deviation, sideslip angle, yaw rate, and vehicle roll angle decreased by 22.6%, 33.9%, 5.5%, and 1.2%, respectively. In the CDC scenario, the truck’s lateral acceleration, sideslip angle, yaw rate, and vehicle roll angle decreased by 7.5%, 46.8%, 8.2%, and 80%, respectively. Additionally, open-loop simulation tests were conducted under fishhook steering conditions for both passenger cars and trucks. The results further validated the effectiveness of the integrated control strategy, demonstrating its ability to significantly improve yaw rate and roll response, thereby enhancing overall vehicle stability under challenging driving conditions.</div>

Inhomogenuous instabilities at large chemical potential in a rainbow-ladder QCD model

In this work we continue our efforts to study the existence of a phase with an inhomogeneous, i.e., spatially varying, chiral condensate in QCD. To this end we employ a previously established method of stability analysis of the two-particle irreducible effective action in a truncation that corresponds to a rainbow-ladder approximation of the quark-gluon interaction of QCD. If the analysis is restricted to homogeneous phases, the phase diagram features a first-order chiral transition in the lower-temperature regime. Performing the stability analysis along the lower-chemical-potential border of the corresponding spinodal region, we find that below a certain temperature the homogeneous chirally symmetric solution is unstable against inhomogeneous condensation. We argue that this instability may persist to chemical potentials above the homogeneous first-order phase boundary, in which case it signals the existence of an inhomogeneous ground state. Our methodology is also applicable for more sophisticated truncations of the QCD effective action. Published by the American Physical Society 2024

Flutter margin research based on system stability analysis methods

Flutter margin research based on system stability analysis methods

Comparison of stability analysis methods for safe design of volcanic rock slope

The performance of the stability chart (SC), limit equilibrium (LE), and finite element (FE) methods for stability analysis of weathered volcanic rock slopes under static and earthquake loads is not fully understood. This research aimed to evaluate the performance of the SC, LE, and FE methods for slope stability analyses by studying a case of a weathered volcanic rock slope at the Leuwikeris Dam diversion tunnel in Indonesia. Site characterisations were carried out to obtain the input parameters for the static and pseudostatic slope stability analyses. The results showed that using various search methods of failure surface and the suggested optimum number of finite elements, multiple non-circular failure surfaces were predicted from the LE and FE methods that were not anticipated in the initial slope design based on the SC method. The location and shape of the failure surfaces from the LE method agreed with those from the FE method. The difference between the Fs values from the static LE analysis and those from the static FE analyses was less than 14%, but the discrepancy increased up to 78% in the pseudostatic analyses. This study highlights the importance of validating the results from one method with the other methods to prevent slope failures.

Stability Analysis of Surface Wellhead Retention in Offshore Exploration Wells

Abstract When offshore exploration wells are carried out, a narrow operating window and prolonged construction period may be encountered, which may lead to the evacuation of the drilling platform. The conductor will be left freestanding in the sea water, posing a great risk to wellhead stability. In this paper, based on finite element simulation of offshore exploratory well freestanding conductors, the stability analysis method is built and evaluation of a well is carried out. It is concluded that in 1 year return period and sea conditions by hanging load return period of 10 years of sea condition, the stability all meet the conditions, but there in 10 years return period of sea state by hanging load and 50 years return period of sea condition did not meet the requirements of stability. In cases where stability requirements are not met, alternative means of retaining the wellhead are recommended. This study has certain guiding significance for the safe and efficient operation of offshore exploration wells.

Fluorescence labeling-based differential scanning fluorimetry, an effective method for protein thermal stability and protein-compound binding analysis

Differential scanning fluorimetry (DSF) is widely used to assess protein thermal stability and protein-ligand interaction. However, its utility is often limited by the presence of detergents, which can affect hydrophobic binding. To tackle this issue, we developed an effective fluorescence-labeled DSF (FL-DSF) technique that tracks protein denaturation by monitoring the labeling fluorescence decrease, thus overcoming challenges typically encountered with traditional DSF methods. In this research, FL-DSF was first validated using Peroxisome Proliferators-Activated Receptor γ (PPARγ), Retinoid X Receptor α (RXRα), and Lysozyme, confirming its accuracy in determining melting curves. Expectedly, FL-DSF also exhibited strong compatibility with detergents in our investigations. Besides this, a new calculation method was proposed to characterize the protein denaturation process and evaluate protein-ligand binding. This mathematical model goes beyond traditional approaches, which simply treated the melting temperature (TM) shift as a concentration-dependent variable. Instead, it comprehensively incorporates the influence of irreversible denaturation-induced native protein loss on the equilibrium of protein-ligand binding. This methodology was successfully applied into the evaluation of binding affinity for 2 classical binding systems of PPARγ-Rosiglitazone and RXRα-CD3254. It was also utilized for the following binding screening studies, leading to the discovery of promising ligands for PPARγ, RXRα, and Lysozyme.

Research on Graph Multi-Attention Neural Network for Power System Transient Stability Assessment

Abstract Diagnosing the stability of power grids based on artificial intelligence technology is a research trend. The existing artificial intelligence stability analysis methods rely on a large number of fault case data, while the graph neural network method ignores the correlation characteristics of nodes themselves and the correlation of long-distance nodes. In order to solve the problems, the graph multi-attention neural network (GMANN) was proposed. The self-attention, which characterizes the correlation between different state quantities of a single node, is proposed, firstly. Then, long-distance association attention, which represents the correlation of distant nodes in the power grid, was proposed. The long-distance correlation attention and the adjacent correlation attention in graph attention network are fused to form a global attention that reflects the global importance of the power grid. The channel attention that characterizes the importance of different pooling methods of graph convolutional network is extracted and used to obtain the importance of different convolution operations. Finally, based on the multi-source attention fusion strategy, global attention and channel attention are embedded in the graph attention neural network to form a multi-level evaluation model to achieve power grid stability evaluation efficiently guided by multiple attentions. The proposed GMANN is verified based on simulated fault cases obtained from the 10-machine 39-node system in New England. The results show that the accuracy of the GMANN can reach 97.34%, which is better than other methods. And the missed judgment rate of important indicators is significantly better than other methods.

Impedance modeling and quantitative stability analysis of grid-connected voltage source converters under complex unbalanced conditions

The stability issues caused by voltage source converters (VSCs), which are commonly used in renewable energy systems, are investigated in this paper. Much literature has investigated the impedance models and quantitative stability analysis for converters under the weak and unbalanced grid. However, on the one hand, harmonic-transfer-function (HTF)-based modeling methods are complex, and the established infinite-order models may suffer from unreasonable truncation. On the other hand, these existing impedance models without considering all unbalance factors are inaccurate. Both of these may bring wrong stability analysis results. Therefore, this paper proposes a simple impedance extension method and considers all unbalance factors to derive the impedance model of the converter. However, due to the established higher-order impedance model, the traditional impedance-ratio based stability analysis method is not applicable to multi-input multi-output (MIMO) systems. The commonly used eigenvalue-based GNC and diagonalization-based methods applicable to MIMO systems are cumbersome and not suitable for quantitative analysis. Therefore, in this paper, a quantitative analysis tool of system stability based on the phase-frequency characteristics of determinants is developed. Then, stability regions in the multi-parameter space are obtained. Finally, the established impedance model and the quantitative analysis results are validated via both simulations and hardware experiments.© 2017 Elsevier Inc. All rights reserved.

A new combined finite-discrete element method for stability analysis of soil-rock mixture slopes

PurposeThe purpose of this paper is to propose a new combined finite-discrete element method (FDEM) to analyze the mechanical properties, failure behavior and slope stability of soil rock mixtures (SRM), in which the rocks within the SRM model have shape randomness, size randomness and spatial distribution randomness.Design/methodology/approachBased on the modeling method of heterogeneous rocks, the SRM numerical model can be built and by adjusting the boundary between soil and rock, an SRM numerical model with any rock content can be obtained. The reliability and robustness of the new modeling method can be verified by uniaxial compression simulation. In addition, this paper investigates the effects of rock topology, rock content, slope height and slope inclination on the stability of SRM slopes.FindingsInvestigations of the influences of rock content, slope height and slope inclination of SRM slopes showed that the slope height had little effect on the failure mode. The influences of rock content and slope inclination on the slope failure mode were significant. With increasing rock content and slope dip angle, SRM slopes gradually transitioned from a single shear failure mode to a multi-shear fracture failure mode, and shear fractures showed irregular and bifurcated characteristics in which the cut-off values of rock content and slope inclination were 20% and 80°, respectively.Originality/valueThis paper proposed a new modeling method for SRMs based on FDEM, with rocks having random shapes, sizes and spatial distributions.