Stability Problem Research Articles

Analysis of Factors Obstacling Construction Work in the Tojo Una-Una Islands Region

The implementation of construction activities in the island region of Tojo Una-Una Regency tends to be very vulnerable to the risk of delays, even failure, due to obstacles experienced by implementing parties in the field. The aim of this research is to find out the factors that hinder construction work in the island region of Tojo Una-Una Regency and to find out the efforts made by implementing parties to overcome these obstacles. This factor is the biggest factor hampering construction work in the island region of Tojo Una-Una Regency compared to other factors. Efforts made to overcome these obstacles include implementing human resource management for construction workers properly, building a collaborative network with a number of construction material suppliers, acting decisively against owners who are late in making payments, improving the coordination system between contractors and owners, carrying out modernization and regular maintenance of equipment. construction, establishing good communication with the environment around the project, conducting in-depth studies and handling soil stability problems at the project site, and scheduling visits and sending resources to the project site appropriately.

Round-robin scheduling protocol-based stabilization for discrete-time Markov jumping neural networks

This paper focuses on the stabilization problem of discrete-time Markov jumping neural networks (DMJNNs) under communication constraints between the actuators and the remote controller. To reduce the communication burden, a round-robin scheduling protocol is introduced to allocate the right to a single actuator to exclusively use the communication channel at a given time while ensuring that multiple nodes can take turns to occupy the channel for signal transmission. Two criteria for stochastic analysis of the closed-loop network model are presented based on different assumptions of the activation functions. Then, numerically tractable design methods for the required controller gains are developed. Finally, the three-mode DMJNN model is used as an example to illustrate the complementarity and effectiveness of the presented analysis results and design methods.

Intelligent Power System Stability Assessment and Dominant Instability Mode Identification Using Integrated Active Deep Learning.

Simulation analysis is critical for identifying possible hazards and ensuring secure operation of power systems. In practice, large-disturbance rotor angle stability and voltage stability are two frequently intertwined stability problems. Accurately identifying the dominant instability mode (DIM) between them is important for directing power system emergency control action formulation. However, DIM identification has always relied on human expertise. This article proposes an intelligent DIM identification framework that can discriminate among stable status, rotor angle instability, and voltage instability based on active deep learning (ADL). To reduce human expert efforts required to label the DIM dataset when building DL models, a two-stage batch-mode integrated ADL query strategy (preselection and clustering) is designed for the framework. It samples only the most helpful samples to label in each iteration and considers both information contents and diversity in them to improve query efficiency, significantly reducing the required number of labeled samples. Case studies conducted on a benchmark power system (China Electric Power Research Institute (CEPRI) 36-bus system) and a practical large-area power system (Northeast China Power System) reveal that the proposed approach outperforms conventional methods in terms of accuracy, label efficiency, scalability, and adaptability to operational variability.

Research on Voltage Coordinated and Stability Control of Condensers Based on Reactive Power Replacement

Abstract In this research, we investigated condenser voltage coordination and stability control systems by analyzing voltage coordinated control mode among excitation, voltage coordination and stability as well as automatic-voltage reactive power control systems. By using dynamic excitation regulation and steady-state regional voltage source control replacement, dynamic reactive power quickly output under fault condition as well as optimized regional reactive power under steady state were realized. The correctness and practicability of the proposed strategy was verified through engineering application. Adopting the reactive power displacement of voltage coordination control system to solve local voltage instability problem after UHV DC blocking. The proposed method realized multi-time scale emergency, recovery and steady-state control of the system under steady and dynamic states.

Experimental study and prediction method of solid destabilization and production in deep carbonate reservoir during mining

Wellbore instability is one of the significant challenges in the drilling engineering and during the development of carbonate reservoirs, especially with open-hole completion. The problems of wellbore instability such as downhole collapse and silt deposit in the fractured carbonate reservoir of Tarim Basin (Ordovician) are severe. Solid destabilization and production (SDP) was proposed to describe this engineering problem of carbonate reservoirs. To clarify the mechanism and mitigate potential borehole instability problems, we conducted particle size distribution (PSD) analysis, X-ray diffraction (XRD) analysis, triaxial compression tests, and micro-scale sand production tests based on data analysis. We found that the rock fragments and silt in the wellbore came from two sources: one from the wellbore collapse in the upper unplugged layers and the other from the production of sand particles carried by the fluid in the productive layers. Based on the experimental study, a novel method combining a geomechanical model and microscopic sand production model was proposed to predict wellbore instability and analyze its influencing factors. The critical condition and failure zone predicted by the prediction model fit well with the field observations. According to the prediction results, the management and prevention measures of wellbore instability in carbonate reservoirs were proposed. It is suggested to optimize the well track in new drilling wells while upgrading the production system in old wells. This study is of great guiding significance for the optimization of carbonate solid control and it improves the understanding of the sand production problems in carbonate reservoirs.

Automatic control of constant temperature and humidity in building air conditioning systems based on frequency domain analysis

How to solve their automatic control of constant temperature and humidity gradually becomes a research hotspot as the continuous upgrading of air conditioning systems. This study aims to optimize the traditional proportional-integral-differential controller for improvement to solve the time-delay instability phenomenon in temperature and humidity control. The objective of this study is to optimize existing proportional-integral-differential controllers to improve the time-delay instability problem that is common in temperature and humidity control. Firstly, it treats the controlled object as a first-order and second-order system with time-delay characteristics. Next, the Smith predictor controller is generalized equivalent to ensure that the equivalent system does not contain time-delay. Finally, an analysis of the first-order and second-order closed-loop control system is conducted by combining Smith predictive controller and proportional-integral-differential controller. The system achieves the goal of automatic control of constant temperature and humidity by adjusting the control parameters. The experiment showcased that the temperature control time of the proposed control scheme under first-order and second-order time-delays was 16 s and 3 s, respectively. Meanwhile, the humidity control time was 14 s and 13 s, respectively. In practical applications, the proposed control scheme achieved good control effects in all four seasons. This indicates that the controller designed in this study possesses good control performance. It also can achieve the goal of constant temperature and humidity control. This can provide technical support for the automation control of air conditioning systems.

System model of risks and trees of alternative solutions for improving the logistics chain at a manufacturing enterprise

The subject of this article is the decision-making processes for improving the elements of the supply chain of a manufacturing enterprise under conditions of uncertainty and risks. The purpose of the research is to reduce the time and cost of in supply and distribution of products of manufacturing enterprises by considering possible risks through making rational management decisions. The article addresses the following tasks: examination of the characteristics of supply chain elements; investigation of the main problems of supply and distribution management and identification of ways to solve them; development of a systemic model of logistic risks for a manufacturing enterprise; and formation of decision trees for alternative decisions in strategic supply chain management at manufacturing enterprises. The methods applied include a systems approach, structural decomposition methods, a risk-oriented approach. The following results were obtained: features and problems of supply chain elements such as supply, production, storage, and distribution were examined and identified; main supply chain management tasks were investigated and solutions identified; problems in warehouse management were pinpointed; internal and external supply risks were identified; a systemic model of logistic risks for a manufacturing enterprise was formed, which main components are logistic problems, partial risks, their consequences, and possible management decisions to mitigate risks; decision trees were built for problems of raw material supply instability and transportation bottlenecks and delays; an alternative decision diagram was constructed for an illustrative example. Conclusions: To overcome the problem of raw material supply instability, it is recommended to develop diversification of supply sources, stock reservation, and the use of alternative transport routes. Building alternative decision trees in strategic management is an effective tool for making rational decisions by manufacturing enterprises in complex conditions of uncertainty and risks. They help to analyze alternatives and their consequences to choose a path to optimize the supply chain.

Investigation of Wellbore Instability in Southern Rumaila Oil Field

This study aims to address the issue by providing valuable insights into the factors contributing to the wellbore instability and proposing effective measures to mitigate the problem in the southern part of the Rumaila oil field. A comprehensive one-dimensional mechanical earth model (1D MEM) was developed by utilizing various logs data from 4 wells across the south part of this field, including gamma ray, bit size, caliper, bulk density, and sonic compression and shear logs. The model was validated with laboratory tests, including Brazilin and Triaxial tests, as well as repeated formation tests. To analyze the wellbore stability, three different failure criteria, namely Mohr-Coulomb, Mogi-Coulomb, and Modified lade, were employed. The results indicated that the Mogi-Coulomb criterion was the most accurate failure criterion in predicting rock failure. Wellbore instability problems had been observed across the shale sections throughout the Rumaila oil field, particularly through Tanuma, Khasib, top and bottom of Ahmadi, Nahr Umr, and Upper Shale members and Middle Shale members of Zubair formations. The 1D MEM results indicated that Shaly formations exhibited low stiffness rocks (low Young's Modulus (YME)), low rock strength, and high Poisson's ratio (PR), suggesting potential challenges related to wellbore instability in the Tanuma, top and bottom of Ahmadi, Nahr-Umr, and Zubair formations. A sensitivity analysis was performed to determine the safest mud weight and the optimum well trajectory for future drilling operations. According to the updated mud window of this field in 2023, the pressure in the Mishrif and Zubair formations was reinforced by injection wells, as it was noted that the pressure behavior shifted from depletion (2000 Psi). Based on the findings of this study, the good inclination of (0-25°) can be drilled with the mud weight of 1.24-1.26 sg, while the good inclination of (25-40°) can be drilled with the mud weight of 1.28-1.30 sg in all directions (i.e., all azimuths). The stress regime in most of the formations was found to be a strike-slip to a normal fault regime. The findings of this study can significantly benefit the oil industry and enhance overall productivity.

Semi-time-dependent stabilization results for asynchronously switched systems: An extended persistent dwell time switching strategy involving admissible transition information

This study investigates the stabilization problem for a kind of continuous-time asynchronously switched systems via a set of edge- or mode-dependent state-feedback controllers. To this end, an innovative switching strategy of admissible chain-dependent (or admissible edge-dependent) persistent dwell time property is presented by injecting the admissible transition chain (or admissible transition edge) notion into the existing persistent dwell time concept. Based on the admissible transition edges in a directed graph reported in the literature, the corresponding admissible transition chains can be determined. The individual allocation of transition weights for each admissible transition chain makes the presented admissible chain-dependent persistent dwell time switching less conservative than the other presented admissible edge-dependent persistent dwell time and the already existing mode-dependent persistent dwell time switching. Further, different from the Lyapunov functions commonly used in previous asynchronous stabilization works, a new semi-time-dependent Lyapunov function in a unique form that fits the nature of the discussed systems is suggested to provide a broader family of allowable switching signals. By the introduced switching and Lyapunov function approaches, new stability and stabilization criteria are formulated, through which the expected edge- or mode-dependent state-feedback controllers are devised. At last, the validity and applicability of the obtained stabilization solutions are demonstrated by a numerical example and a practical thermal system.

Improving both performance and stability of n-type organic semiconductors by vitamin C.

Organic semiconductors (OSCs) are one of the most promising candidates for flexible, wearable and large-area electronics. However, the development of n-type OSCs has been severely held back due to the poor stability of their most candidates, that is, the intrinsically high reactivity of negatively charged polarons to oxygen and water. Here we demonstrate a general strategy based on vitamin C to stabilize n-type OSCs, remarkably improving the performance and stability of their device, for example, organic field-effect transistors. Vitamin C scavenges reactive oxygen species and inhibits their generation by sacrificial oxidation and non-sacrificial triplet quenching in a cascade process, which not only lastingly prevents molecular structure from oxidation damage but also passivates the latent electron traps to stabilize electron transport. This study presents a way to overcome the long-standing stability problem of n-type OSCs and devices.

Improvement of the prediction of the flexural buckling resistance of hot-rolled mild and high-strength steel members

The determination of the bearing capacity of a member under compression, presenting an initial out-of-straightness and residual stresses resulting from the production process, is a stability problem governed by the geometry of the member and the mechanical properties of its constitutive material. Amongst these, the yield strength plays a key role. Indeed, it has a direct impact on the spread of yielding in the member but, also, the detrimental effect of geometrical and material imperfections decreases as the yield strength increases. The effect of these initial imperfections is considered by an imperfection factor α in the design recommendations provided in EN1993–1-1. However, the current and new upcoming versions of this norm give a stepwise evolution of this imperfection as a function of yield strength by only distinguishing grades lower than S460 from the ones equal/higher than S460. The present paper aims to briefly summarize the existing studies on this topic, to assess the recommendations of current and new upcoming versions of EN1993–1-1 and the models reported in the literature and, finally, to suggest a modified imperfection factor for hot-rolled sections (H-shape and I-shape) for already existing grades (up to S500) but also for grades up to S690, which do not exist yet for this section typology in the European steel market, to evaluate the structural benefit of developing them.

Active filter parameter tuning method for harmonic voltage mitigation in wind power plants

It is challenging to determine the active filter control factors in wind power plants (WPP) to obtain effective harmonic voltage mitigation and avoid over-modulation or system instability problems caused by overlarge feedforward or feedback gains. To address this issue, an active filter tuning (AFT) method is proposed in this paper to offer a common parameter tuning and stability assessment strategy for both current-controlled and voltage-controlled harmonic impedance reshaping (HIR) methods by introducing a coordination factor including different weight coefficients for system stability margin, wind turbine (WT) harmonic suppression, and grid harmonic mitigation. The superiority of the proposed method is verified in a 20 MW WPP with four cases considering both WT harmonic voltage amplification and grid voltage amplification. Compared to previous methods, the AFT-based HIR method achieves a more flexible balance between system stability and harmonic voltage mitigation, obtaining better performance in WT harmonic suppression, grid harmonic suppression, system robustness, and transient response.

Time-varying equivalent circuit for dynamically modulated dielectric slabs and its implications for stability analysis.

Equivalent circuits (ECs) have played an instrumental role in analyzing and modeling distributed electromagnetic structures for many decades, owing to their intrinsic simplicity and the valuable intuition and physical insights they provide. Here, we envision what we believe to be a novel class of ECs featuring linear time-varying (LTV) circuit elements to harness the power of EC analysis for studying LTV structures, particularly LTV dielectric slabs. Our time-varying equivalent circuit (TVEC)-consisting of infinitely many time-varying LC resonators interconnected in either series or parallel-is rigorously derived and exact, with closed-form expressions for the circuit elements. Its convenient form, enabled by a judicious use of Mittag-Leffler expansion, simplifies the analysis of LTV slabs experiencing various resonant and harmonic phenomena. We demonstrate this point by applying our TVEC to the problem of parametric instability in linear time-periodic slabs. Despite its immense importance, instability has been largely neglected in the literature on periodically modulated structures, mainly due to the inherent complexity of problems involving partial differential equations with time-periodic coefficients. Time-periodic circuits, on the other hand, enjoy an abundance of mathematical tools and methods in the form of the theory of Hill's equation. We utilize this rich theory to investigate the nature of parametric instability in linear time-periodic slabs. Numerical results are then presented to verify these findings. Our TVEC is simple, applicable to any form of temporal modulation (not just periodic), and potentially extensible to other geometries, making it likely to have a significant impact on a multitude of hotly researched LTV topics.

Fast analysis approach for instability problems of thin shells utilizing ANNs and a Bayesian regularization back-propagation algorithm

Abstract This research develops a data-driven methodology for structural instability problems with highly nonlinear, difficult, noisy, and small data. A fast analysis and prediction (FAP) approach for instability problems of thin shells is first proposed. This approach contains two phases: the fast numerical analysis and the pure prediction utilizing artificial neural networks (ANNs) incorporated with the Bayesian regularization (B-R) algorithm as follows: (1) in Phase 1 (the fast numerical analysis), post-buckling analysis is conducted utilizing a minor amount of load steps. The load–displacement relation achieved from Phase 1 is not exact because of the small number of load steps utilized; (2) in Phase 2 (the prediction), the loads and deflections achieved from Phase 1 were employed as the data for training ANNs. The trained networks, including the load and displacement networks, were employed to fast predict loads and deflections at any step of the post-buckling analysis. After utilizing Phase 2, a smooth, complete and exact load–displacement curve was achieved. In Phase 1, the available formulation for post-buckling analysis of thin shells in the literature was utilized. Five popular types of instabilities chosen to confirm the effectiveness and exactness of the FAP were snap-through, snap-back, softening–hardening, kink instabilities, and delamination buckling and post-buckling of composites. The high exactness and effectiveness of the FAP were confirmed in the numerical verification section. The present approach saves a huge computation compared to the other ones. It was found that ANNs incorporated with the B-R algorithm have notable advantages compared to numerous neural networks. The proposed approach is applicable to simulations or experiments where data are “expensive”, highly nonlinear, difficult, and limited. Utilizing the proposed approach for these fields can dramatically save time and money.

The impact of the establishment of the cross-border balancing market on the integration of RES into the regional electricity grid

Nowadays, it has become of great importance to obtain electricity from renewable, clean sources that do not pollute the nature. Wind power plants and photovoltaic-based solar power plants, which are among the leading renewable energy technologies, pose difficulties in monitoring the system for transmission system operators because their production is intermittent and not always continuous. Production from these sources varies with changing weather conditions and can be difficult to predict. Although new renewable capacities are available, including in the power system, the problem of intermittency of meteorological uncertainty is a major problem for the system stability of the power grid. The electricity obtained from RES based on intermittent wind and solar energy can vary significantly in a short time depending on changing weather conditions. The greater the share of these intermittent power supplies connected to the grid, the greater the risk of instability in the system. In this sense, integrating Turkey's large capacity in wind, solar and hydroelectric energy with the energy system of neighboring countries will greatly increase system reliability. Establishing regional energy markets and cross-border electricity collaborations are of great importance for the integration of this discrete renewable energy capacity into the system. In this study, Turkey's contribution to the integration of renewable resources into the cross-border power balancing market and regional load transfer is investigated. The electrical load transfer potential was examined in the light of the current capacity and planned future capacity increases, and the benefits and necessity of the system to be installed were revealed.

A note on boundary feedback stabilization for degenerate parabolic equations in multi-dimensional domains

Abstract In this paper, we are concerned with the problem of stabilization of a degenerate parabolic equation with a Dirichlet control, evolving in bounded domain 𝓞 ⊂ ℝ d , d ≥ 2. We apply the proportional control design technique based on the spectrum of the linear operator which governs the evolution equation. The stabilizing feedback control, we design here, is linear, of finite-dimensional structure, easily manageable from the computational point of view.

Characterisation of the internal friction angle of waste rock material from large triaxial tests using the contact dynamics method

ABSTRACT The Chilean copper mining industry generates large amounts of waste rock materials. These structures must be designed, operated, and closed considering their physical stability. Although these structures generally do not present physical stability problems, superficial failures may occur, where waste rock material is subjected to low confining pressures. The identification of the internal friction angle, necessary for stability calculations, is based on the characterisation of these materials under high confining pressures. This assumption is not representative of the loading conditions in the superficial layers. To address this issue, numerical large-scale triaxial tests, using the contact dynamics method, are performed to identify the internal friction angle of these materials under low confining pressures. To model these material, irregular polyhedrons were generated using statistical data of crushed aggregates, considering the morphology and the particle size distribution from experimental waste rock materials. The proposed numerical approach was validated by comparing it to literature data for confining pressures over 0.5 MPa. Our results indicate that the internal friction angle stabilises at 39° for confining pressures below 0.1 MPa. This study provides important insights into the physical stability of waste rock dumps and contributes to the development of more accurate stability calculations for these structures.

Clinical trial to test the safety of the EVA Nexus surgical platform

BackgroundThe EVA Nexus system offers several technical improvements over its predecessor. The newly designed Aveta cannula system for vitrectomy surgery avoids the need for removal of the valve from the infusion cannula. The chamfered leading edge of the cannula also reduces the insertion force needed. The new EquiPhaco needles in combination with SmartIOP provide excellent anterior chamber stability during phaco-emulsification surgery, enabling to work at lower infusion pressures, and the multiburst phaco mode allows easier removal of hard cataracts. The system offers a secondary active infusion line for independent control of pressure to the anterior and posterior chambers, monitoring of flow rate/reflux and warning of infusion bottle emptying. This study evaluated whether these technical improvements result in improved surgical safety.MethodsIn total, 250 eyes that underwent vitrectomy (53%) or phaco-vitrectomy (47%) using the EVA Nexus system were prospectively included. The occurrence of intraoperative adverse events was compared to that of historically operated eyes using the EVA system.ResultsThe average age of the patients was 63 years. A total of 33% of the patients were operated on for retinal detachment, 17% for macular pucker, 11% for treating floaters, 9% for removing silicone oil, 8% for macular hole repair and 22% for other diseases. In 75% of surgeries, 23 G instruments were used, and 27 G instruments were used in 25% of cases. Device issues that occurred included priming cycle issues (n = 4), eye pressure stability problems (n = 6) and vitrectome performance issues (n = 1), all of which in the first 100 patients who were included and were fixed with software updates. The frequency of surgical complications in the anterior segment was lower than that in the historically recorded surgical reports. Intraoperative events in the posterior segment included hemorrhage from retinal vessels, choroidal hematoma, iatrogenic retinal damage/tear, and subchoroidal infusion. Again, these events occurred rarely and less frequently than in the historical surgical reports.ConclusionsThe EVA Nexus provides a surgical platform that reduces the incidence of intraoperative adverse events and iatrogenic complications in both anterior and posterior segment surgery. This could increase surgical safety during cataract and vitrectomy surgery.Trial Registration number Clinicaltrials.gov: NCT05229094 Data 22/5/2021.

High-entropy perovskite quantum dots of rare earth synergy with excellent luminescence stability via high-energy ball milling

The problem of low stability and high lead content limit the commercial development of halide perovskite. In this paper, the high-energy ball milling is used to rapidly and efficiently synthesize high-entropy Cs(Pb1/5Mn1/5Ni1/5Zn1/5Yb1/5)Cl3 quantum dots (QDs), the introduction of high-entropy and rare earth ions reduces lead content, increases mixing entropy, and synergistically enhances the photoluminescence (PL) intensity and stability of QDs with other ions. Because the increase of entropy enhances the stability, the QDs still have 70 % PL intensity after 60 days of placement. After the QDs are exposed to the ultraviolet lamp for 8 hours, the PL intensity maintains at 67.1 % due to the loss of ligand. Ionic bonds are easily broken in water, so after soaking in water for 8 hours, the PL intensity of the QDs keeps at 32 %. The thermal stability of QDs is maintained well because of physical and chemical stability of rare earth ions. Since ethanol dissolves the ligands on the surface of the QDs, the non-radiative recombination is enhanced, so the PL intensity of QDs remains at 59 % after soaking for 8 hours. This paper provides a new way that further enhances the stability and solves high lead content of all-inorganic perovskite materials.

Optical flow vector of elastic waves in transversely isotropic media

The propagation direction of the wavefield is particularly important for migration imaging in the reverse-time migration (RTM) of elastic waves in transversely isotropic (TI) media. However, due to the problem of the computational instability of the Poynting vector, the wave field propagation direction estimated based on the Poynting vector method has errors and cannot accurately indicate the real propagation direction of the elastic wavefield. To solve this problem, a method for calculating the optical flow vector of elastic waves in TI media is developed to obtain the propagation direction. The optical flow vector of elastic waves in TI media is determined by applying the spatial and temporal derivatives of the wavefield at each time step under the assumption that the wavefields are almost the same at subsequent time steps and are smooth in the spatial direction. As the additional smoothing item is added and the multiple iterative algorithm is introduced in calculating the optical flow vector, the direction is calculated more accurately than the Poynting vector. Based on the optical flow vectors, we can separate the source wavefield and receiver wavefield into four directions: up-going, down-going, left-going, and right-going wavefields, respectively, and finally perform elastic reverse-time migration (ERTM) imaging based on the optical flow vector traveling-wave separation. We use a layered model and the BP model to test our method. The testing results demonstrate that the optical flow vector can overcome the Poynting vector limitations and obtain more accurate and reliable information regarding the direction of elastic wave propagation in TI media, as well as precisely separate the wavefields. The separated wavefields for migration effectively improve the quality of the ERTM.