Stability Evaluation Method Research Articles

Performance evaluation and state recognition method based on non‐parametric estimation algorithm for photovoltaic arrays

AbstractWith the rapid development of photovoltaic (PV) power generation, state recognition of PV arrays is of great significance to its intelligent operation and maintenance. But the random fluctuation of PV power output leads to the obvious uncertainty for performance calculation of PV arrays; this paper proposes an evaluation method of PV arrays. Firstly, the performance calculation method and its distribution model were proposed by the kernel density estimation (KDE) method. Secondly, the probability density distribution (PDD) of different indicators was analyzed to determine the suitable observation indicator so as to introduce the stability indicator, from which the benchmark array was selected. Finally, the state recognition of PV arrays was achieved. The main conclusions and innovations of this paper are the stability evaluation method of PV arrays based on the non‐parameter estimation method and the effective operating state recognition method for PV arrays. The proposed method was proven to be more reliable by comparing it to the power generation ranking method (PGRM). The effectiveness was verified by comparing the statistical and real‐time distribution of the performance ratio, and the excess rate of different confidence levels and Euclidean distance were introduced to demonstrate the accuracy of the proposed state recognition method.

Construction and Application of an Intelligent Roof Stability Evaluation System for the Roof-Cutting Non-Pillar Mining Method

In order to sustainably use coal resources and reduce coal mine accidents, the stability evaluation of roadway roofs is particularly important. The existing methods of roof stability evaluation and control application are greatly disjointed, the relationship between roof stability evaluation and early warning control is ignored, and an intelligent evaluation and calculation control system is lacking. Based on the successful application of the roof-cutting non-pillar mining method in various engineering geology and mining conditions, the roof stability evaluation system, mobile intelligent computing system, and engineering application research are carried out. An evaluation index system for roof stability in the roof-cutting non-pillar mining method is established, including the roof rock integrity and the roof-surrounding rock displacement. A comprehensive evaluation method for roof stability grades is proposed based on the coupling of evaluation index grading criteria and improved analytic hierarchy process (AHP) weight assignment. A handheld mobile intelligent platform for roof stability evaluation, roof hazard zone, and control suggestion is developed. The research results have been applied in the coal mine of Hecaogou with good outcomes. This intelligent stability evaluation system will provide an economical and effective approach to achieving sustainable use of coal resources.

Stability and adaptability of wheat cultivars with low cadmium accumulation based on farmland trials

Planting wheat cultivars with low cadmium (Cd) accumulation could help overcome grain Cd contamination. However, the variation in low-Cd accumulation characteristics as influenced by genotype and the environment is unclear. To explore the stability and adaptability of wheat cultivars with low-Cd accumulation in different environments, we analyzed characteristics based on bioconcentration factor (BCF) and yield data obtained from thirteen low-Cd cultivars grown in ten locations. An additive main effect and multiplicative interaction (AMMI) model with homogeneous grouping based on location type successfully captured the effects of genotype, the environment, and their interaction on low-Cd accumulation stability, with environmental effects (49.62–68.45%) having the greatest influence on the stability of low-Cd accumulation cultivar characteristics. A genotype plus genotype-by-environment interaction (GGE) biplot accurately and intuitively illustrated the adaptability of low-Cd-accumulating wheat cultivars, indicating that the best linear unbiased prediction (BLUP) had a more plausible variation explaining the variance than the means. Here, we identify the cultivars LX99, YN999, JM229, and JM22 as having the best stability and adaptability for low-Cd accumulation by using a heterogeneous linear mixed model with BLUP calculation, combined with cluster and weight analysis. Planting these wheat cultivars with low-Cd accumulation can enable the safe utilization of lightly Cd-contaminated farmland with no reduction in yield. This study extends the application of stability evaluation methods in environmental studies and provides a reference for exploring the stability of other cultivars with low heavy metal accumulation.

Refugee Resettlement by Extending Group Multirole Assignment

The World Bank estimates that the number of refugees worldwide will reach 140 million by 2050 due to global warming and local wars. Considering the rapid increase in the number of refugees, an efficient and feasible assignment method is required for refugee resettlement. This article formalizes the refugee resettlement issue using the Environments-Classes, Agents, Roles, Groups, and Objects (E-CARGO) model. A novel solution is designed for Refugee reSettling (RS) by extending the Group MultiRole Assignment (GMRA), which applies the agent stability evaluation method as a feedback mechanism while optimally resettling refugees. With this proposed solution, decision-makers can swiftly resettle refugees from multiple suffering countries while appropriately ensuring host countries’ benefit. Finally, large-scale simulation experiments based on the Python PuLP platform are carried out to demonstrate the practicability and robustness of the proposed solution. The simulation results provide a solid decision-making reference for the leaders of the world.

Influence of Hydrodynamic Pore Pressure Damage on the Performance of Hot-Mixed Renewable Asphalt Mixture

For evaluating the water stability of hot-mixed renewable asphalt mixture (HRM), the traditional methods are all tested under still water conditions. Except for damage in still water conditions, the hydrodynamic pore pressure generated by the tire driving on the surface water has a great impact. Thus, the RAP contents of the HRMs were designed at 0%, 30%, 45% and 60% with AC-25 gradation. Then, the self-designed evaluation methods of water stability and dynamic modulus were studied. Finally, the mechanism of the influence of hydrodynamic pore pressure damage on HRMs was studied. The results show that the water stability of HRM containing 30% RAP is equivalent to that of 45% RAP, and the water stability of HRM containing 60% RAP decreases significantly. The Contabro test after MIST treatment can be used as an evaluation method for hydrodynamic pore pressure damage on HRM. Low-speed, heavy-load traffic and larger RAP content have greater damage to the mixture after hydrodynamic pore pressure damage. The performance differences between the aged bitumen and pure bitumen, as well as the aged minerals and new minerals, are continuing to be enlarged in hydrodynamic pore pressure conditions, finally affecting the water stability and dynamic modulus of the HRMs.

Cloud-based Connected Vehicle Control under Time-Varying Delay: Stability Analysis and Controller Synthesis

The emergence of connected vehicles and cloud-based control technologies promise great benefits to transportation systems. For practical application, time-varying delay from vehicular communication and edge/cloud computing has a critical influence on the vehicle control performance. To address this problem, this paper focuses on the stability analysis and controller design for connected vehicles under time-varying delay at the cloud-based control architecture. Particularly, connected car-following control and connected path-following control are under consideration as specific examples, where the cloud-unit assigns the control commands. A general switched system model has been established for connected vehicle control, where time-varying delay is imposed on partial system states. For stability analysis, an improved stability condition is proposed for the switched system under general case of time-varying delay with less conservative property compared with existing work. Further, based on Markov process assumption on time-varying delay, a quantitative stability evaluation method is introduced. Then, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathcal {H}_\infty$</tex-math></inline-formula> controller design method has been presented, which incorporates multiple requirements, including stability under delay, control error for safety, and control rapidity. Extensive numerical simulations validate the performance of the proposed control method at multiple traffic scenarios.

Establishment of an efficient and accurate thermal stability evaluation method based on machine vision and its application in PVC thermal degradation

An efficient and accurate PVC thermal stability evaluation method based on machine vision was established.

A gait stability evaluation method based on wearable acceleration sensors.

In this study, an accurate tool is provided for the evaluation of the effect of joint motion effect on gait stability. This quantitative gait evaluation method relies exclusively on the analysis of data acquired using acceleration sensors. First, the acceleration signal of lower limb motion is collected dynamically in real-time through the acceleration sensor. Second, an algorithm based on improved dynamic time warping (DTW) is proposed and used to calculate the gait stability index of the lower limbs. Finally, the effects of different joint braces on gait stability are analyzed. The experimental results show that the joint brace at the ankle and the knee reduces the range of motions of both ankle and knee joints, and a certain impact is exerted on the gait stability. In comparison to the ankle joint brace, the knee joint brace inflicts increased disturbance on the gait stability. Compared to the joint motion of the braced side, which showed a large deviation, the joint motion of the unbraced side was more similar to that of the normal walking process. In this paper, the quantitative evaluation algorithm based on DTW makes the results more intuitive and has potential application value in the evaluation of lower limb dysfunction, clinical training and rehabilitation.

Estimation of Domain of Attraction Based on Equilibrium-Independent Passivity of Power Systems

This paper proposes a method to evaluate the stability of equilibria, corresponding to supply-demand balance for a nonlinear power system, considering the convexity of a potential energy function with respect to an electromagnetic dynamics. The proposed method is devised based on the fact that the entire power system is represented as a feedback system of two subsystems having equilibrium-independent passivity. Because the storage function for equilibrium-independent passivity has the form of the Bregman divergence with respect to the potential energy function, the convex domain of the storage function coincides with that of the potential energy function, which is specific to the power system. Therefore, the domain of attraction is wider if the corresponding equilibrium is located near the center of the convex domain, and narrower if it is located near the boundary of the convex domain. Based on this fact, we also consider improving the stability of the power system by adjusting the inverter parameters. Numerical simulations demonstrate the effectiveness of the proposed stability evaluation method and stability improvement using a power system consisting of three generators.

Mathematical modeling the quarry wall stability under conditions of heavily jointed rocks

Purpose. To develop techniques for estimating the pit wall stability in terms of occurring of a zone of heavily jointed rock mass during ore mining at the Akzhal deposit (Kazakhstan), to work out measures to strengthen the rock opening and to verify the effectiveness of the developed measures. Methodology. The finite element analysis of the rock stress-strain state is implemented on the basis of the elastic-plastic model and the generalized Hoek-Brown failure criterion. The rock mass quality was assessed using the RMR and GSI rating classifications. This made it possible to simulate a zone of intense fracturing by changing the characteristics of the jointed surface. The shear strength reduction procedure was used to determine the safety factor for the quarry wall. Findings. The strain distributions in the rock mass forming the quarry wall have been obtained in terms of the Akzhal polymetallic ore deposit (Kazakhstan). The case of creating a zone of heavily jointed rocks in the area of a tectonic fault was considered. The safety factor of the quarry wall was determined under conditions of increased rock fracturing, as well as after carrying out measures to strengthen the rocks with a hardening solution. Originality. The effect of intense jointness on the pit wall stability is demonstrated. A method for the consistent evaluation of the quarry wall stability is proposed considering the change in the rock properties due to natural factors and artificial reinforcement. It is shown that a change in the joint surface quality due to the hardening injection reduces the shear strains in the sliding zone. Practical value. The pit wall stability was predicted considering the formation of a zone of intense fracturing under mining and geological conditions of the Akzhal deposit. The possibility of testing the effectiveness of rock strengthening measures based on mathematical modeling was shown.

Aeroservoelastic Stability Evaluation for Slender Vehicles Based on the Ground Frequency Response Test

With the increasing bandwidths of servo control systems and decreasing mode frequencies, aeroservoelastic (ASE) stability evaluation has become an essential part of flight vehicle design. However, the theoretical method is limited by the modeling errors of numerical models, and the dry wind tunnel method is limited by the complex design of force controllers. Given these limitations, a novel ASE stability evaluation method for slender vehicles based on the ground frequency response test (FRT) is proposed in this paper. FRTs are implemented for a slender vehicle to obtain the frequency response functions (FRFs) of the real structure and servo control systems. The low-order unsteady aerodynamic FRFs established in physical coordinates are calculated by the quasi-steady aerodynamic derivative method. An ASE open-loop FRF is established for stability evaluation via the Nyquist criterion. Comparison with the theoretical results shows that the proposed method is feasible and accurate for different positions of the inertial measurement unit, different control laws, and different Mach numbers. To deal with the unavoidable influence of hanging supports in the test, an FRF fitting and resynthesis method is used to remove the hanging modes and provide an accurate ASE open-loop FRF with free–free boundary conditions.

Design and stability analysis of bionic end-effector fingers for yarn tube gripping

According to the development demand of automatic yarn tube loading equipment in textile field, a fingertip gripping stability evaluation method is proposed and applied to the end-effector structure design suitable for multi-size yarn tube gripping. Firstly, by studying the human hand mechanism, the tendon type underdrive principle is used to design the rope sheave layout and tendon path of the end-effector finger, and its overall structural design is introduced; secondly, a virtual spring is used to establish an equivalent model of fingertip contact, and the grasping stability is evaluated from the perspective of system potential energy by constructing a stiffness matrix; on this basis, an elliptical curve under geometric constraints is used as the fingertip profile curve, and the release sample is used to Finally, quantitative analysis of gripping stability based on a yarn tube gripping model. The research results lay the foundation for the design of an efficient and reliable yarn tube gripping device. The working principle and design ideas of the bionic end-effector have some implications for the design of robotic end-effectors serving other fields.

Dynamics of offshore wind turbine-seabed foundation under hydrodynamic and aerodynamic loads: A coupled numerical way

The offshore wind power industry has significantly contributed to the production of green energy in China and Europe etc. and made significant contributions to the reduction of carbon emissions. However, the extreme wave and wind loads in typhoon weather bring a great threat to the stability of offshore wind turbines (OWT). It is crucial to understand the dynamic characteristics of OWT and develop reliable methods of stability evaluation to guarantee the stability of OWT. In this study, taking the software FssiCAS as the computational platform, and taking the open-source solver OlaFlow to determine the wave impact on OWT and its seabed foundation, as well as the fluctuating wind theory is applied to estimate the wind load on the turbine blades and tower cylinder, the dynamic characteristics and stability of a monopile OWT with a capacity of 1500 kW in typhoon weather are investigated adopting a coupled way for the first time worldwide. The influence of the complex geometric shape and mass distribution of OWT is considered, and the generalized elastoplastic constitutive model, Pastor-Zienkiewicz-Mark III, is used to describe the complex dynamic behavior of the seabed foundation. The computational results show that the seabed soil within 4–5 m below the seafloor surface becomes liquefied under extreme wind and wave loads, resulting in the horizontal bearing capacity of the seabed foundation being weakened. As a result, the tower cylinder of OWT tilts aside by 0.5°, which exceeds the limit specified in some design codes. Through comparative analysis, it is found that the wind load contributes up to 50% to the lateral displacement of the OWT, and the maximum bending moment in the tower cylinder. It is indicated that wind loads can significantly affect the stability of OWTs. Additionally, this study proves that the software FssiCAS is applicable to evaluate the dynamics and the stability of OWTs under a complex marine dynamic environment. FssiCAS could hopefully become a computational platform for the design of OWTs.

SVM based imbalanced correction method for Power Systems Transient stability evaluation

Due to the requirement of safety and reliability in power systems, unstable samples in the real system are rarely appeared. The evaluation results of the model trained by these imbalance samples have a certain preference. Generally, the imbalance in quantity is taken into account, while the imbalance in quality is ignored. Faced with such a problem, an imbalanced correction method based on support vector machine (SVM) is proposed. Firstly, the classification hyperplane trained by SVM and the normalized Euclidean distance between each sample and the classification hyperplane are calculated so as to obtain their fault severity. Based on this, training samples can be grouped to multilevel sets. Then, the original stacked sparse auto-encoder (SSAE) are pretrained to quantify the imbalance between two classes of samples in multilevel sets. Subsequently, in order to improve the imbalance of training samples, a cost-sensitive correction matrix is generated according to the imbalanced information of multilevel sets. Finally, the loss function of SSAE is modified by cost-sensitive correction matrix to establish the final classifier. Simulation results in IEEE 39-bus system and the realistic regional power system of Eastern China show the high performance of the proposed imbalanced correction method.

A Method for Analyzing the Performance Impact of Imbalanced Binary Data on Machine Learning Models

Machine learning models may not be able to effectively learn and predict from imbalanced data in the fields of machine learning and data mining. This study proposed a method for analyzing the performance impact of imbalanced binary data on machine learning models. It systematically analyzes 1. the relationship between varying performance in machine learning models and imbalance rate (IR); 2. the performance stability of machine learning models on imbalanced binary data. In the proposed method, the imbalanced data augmentation algorithms are first designed to obtain the imbalanced dataset with gradually varying IR. Then, in order to obtain more objective classification results, the evaluation metric AFG, arithmetic mean of area under the receiver operating characteristic curve (AUC), F-measure and G-mean are used to evaluate the classification performance of machine learning models. Finally, based on AFG and coefficient of variation (CV), the performance stability evaluation method of machine learning models is proposed. Experiments of eight widely used machine learning models on 48 different imbalanced datasets demonstrate that the classification performance of machine learning models decreases with the increase of IR on the same imbalanced data. Meanwhile, the classification performances of LR, DT and SVC are unstable, while GNB, BNB, KNN, RF and GBDT are relatively stable and not susceptible to imbalanced data. In particular, the BNB has the most stable classification performance. The Friedman and Nemenyi post hoc statistical tests also confirmed this result. The SMOTE method is used in oversampling-based imbalanced data augmentation, and determining whether other oversampling methods can obtain consistent results needs further research. In the future, an imbalanced data augmentation algorithm based on undersampling and hybrid sampling should be used to analyze the performance impact of imbalanced binary data on machine learning models.

Insight into the anisotropic deformation of landslide sliding zone soil containing directional cracks based on in situ triaxial creep test and numerical simulation

The mechanical behavior of in situ sliding zone soil is unique and is significant for the state identification and prediction of landslides. This study focuses on interpreting the anisotropic deformation observed on the sliding zone soil of the Huangtupo landslide during an in situ triaxial creep test; specifically, the deformation of the A-Surface (towards 35° dip direction) of the soil cube, which points approximately to the landslide sliding orientation, is significantly large. Such anisotropy could be attributed to damaged structure, assumed as pre-existing directional cracks, of the in situ soil. Therefore, a Discrete Element Method (DEM) model containing prefabricated cracks is established to investigate the deforming behavior of compressed soil during in situ creep test on the mesoscopic scale. Results indicated that the specimen's anisotropic deformation is intimately related to the presence of prefabricated cracks. Subjected to the prefabricated cracks, microcracks generated during the loading process of the specimen initiated and developed in a directional way, subsequently forming directed cracks. Then the directed cracks tend to form a complete slip zone. However, due to the insufficient vertical load, the directed cracks were unable to coalesce, and the soil mass did not fail during the in situ creep test. Thereafter, additional load was applied in the simulation model. The directed cracks then merged and a full slip zone formed, and the soil was completely destroyed. As a consequence, the anisotropic characteristics of compressed in situ sliding zone soil can be well explained in view of the cracks development. This study may help perceive the landslide deformation characteristics and facilitate the evaluation and prediction methods of landslide stability.

An electromyography signals-based human-robot collaboration system for human motion intention recognition and realization

• A human-robot collaboration system based on Electromyography (EMG) signals is proposed to learn the position adjustment skills of human body facing the change of external force information, so as to achieve human-robot cooperation. • To improve the recognition accuracy of human motion intention, the coupling effect of human output force and joint angle is considered. • To improve the accuracy and comfort of the collaboration, from the perspective of ergonomics, two evaluation methods of control signal execution efficiency and motion stability are proposed. • A model-free intelligent control mothed is constructed based on DDPG reinforcement learning algorithm, which effectively avoids the selection of control parameters. With the development of manufacturing industry to the directions of personalization and flexibility, the advantages of human-robot collaboration attract more and more attention. In order to enable the robot fully understand human motion intention and play the supervision and guidance role of the human tutor, a human-robot collaboration system based on Electromyography (EMG) signals is proposed. In the investigation, first, aiming at the problems that the coupling effect of output force and joint angle is not considered in the previous research, and the extraction accuracy of force information is poor, the Fast Orthogonal Search (FOS) algorithm is modified to improve the recognition accuracy of motion intention by using the correlation coefficient between the extracted feature signal and the arm output force as the optimization parameter. Moreover, aiming at the problems that the traditional control models cannot balance accurate tracking and comfortable collaboration, and the robot motion stability is poor, two evaluation methods of control signal execution efficiency and motion stability are proposed from the perspective of ergonomics. Afterwards, the human-robot end-to-end collaborative control model based on Deep Deterministic Policy Gradient (DDPG) reinforcement learning algorithm is trained online to improve the accuracy and comfort of the collaboration. As compared with the traditional PD control algorithms based on admittance model, the proposed control method is model-free and intelligent. It effectively avoids the challenge of PD control parameter selection, and behaves good coordination between accurate tracking and comfortable collaboration. Human-robot collaborative sawing experiment shows that the proposed collaboration system can save about 86.2% physical power for the human tutor.

Validity of the frame subtraction method in dynamic postural stability.

BackgroundThe movement of targeted subjects can be calculated using the frame subtraction method. However, the validity of this evaluation method of dynamic postural stability has not been clarified yet. This study aimed to verify the validity of the evaluation method for jump landing using the frame subtraction score based on the ground reaction force (GRF).MethodsTwenty subjects performed single-leg jump landing, and their dynamic postural stability index (DPSI), medial‒lateral stability index (MLSI), anterior‒posterior stability index, and vertical stability index (VSI) were calculated from the GRF. Simultaneously, motion images were captured using digital video cameras in the sagittal and frontal planes. After the motion images were analyzed using the frame subtraction method, the frame subtraction scores in the frontal, sagittal, and combined planes were calculated. To confirm its validity, the relationship between the frame subtraction scores and GRF parameters was investigated using Pearson's correlation analysis.ResultsThe frame subtraction scores in the frontal and combined planes were significantly correlated with the DPSI, MLSI, and VSI (r = 0.46–0.75, P < 0.05).ConclusionsTherefore, the frame subtraction method could be applied to the evaluation of dynamic postural stability. Markerless systems are deemed useful in clinical practice.

Research on the excavation stability evaluation method of Chaqishan ancient landslide in China

It is well known that the deformation and failure during the slope excavation often depends on the excavation height and slope rate. Based on the theory of loading and unloading response ratio, the present study established an evaluation model of the excavation dynamic load-increasing displacement response ratio and created the instability criterion. During the excavation, the stability law of the Chaqishan ancient landslide was analyzed using the Midas GTS NX finite element software, and four slope excavation schemes were redesigned. The results show that, the variation law of the excavation dynamic load-increasing displacement response ratio was consistent with the evolution law of stability coefficient, and there was an obvious negative correlation between them. Therefore, the stability variation law in the slope excavation could be evaluated using the evaluation model of excavation dynamic load-increasing displacement response ratio.

Stability Evaluation Method and Support Structure Optimization of Weak and Fractured Slate Tunnel

Stability Evaluation Method and Support Structure Optimization of Weak and Fractured Slate Tunnel