Accidental Failure Research Articles

Distributed Finite-Time Secondary Frequency Control of Islanded Microgrids With Enhanced Operational Flexibility

Consensus-based control has been widely applied in the frequency/voltage restoration and power sharing of microgrids. Considering the existence of plug-and-play devices and accidental communication failures in microgrids, the physical and cyber structure of a microgrid may be time-varying, where the performance of traditional consensus-based control methods under ideal cases may not be guaranteed. This article proposed a novel finite-time consensus-based secondary frequency control strategy, i.e., a control strategy with finite-time convergence performance. The convergence time of the proposed control strategy is independent of both the structure and operation states of the microgrid, which guarantees the effectiveness of the control strategy under flexible operating conditions. Moreover, a detailed performance analysis of the finite-time control strategy is presented, and an optimal design method of the control parameters is developed, which significantly improves the performance of the finite-time control strategy. The flexibility of the proposed control strategy, as well as the effectiveness of the optimal design method, is verified by both simulation and experimental results.

Transient Responses Evaluation of FPSO with Different Failure Scenarios of Mooring Lines

During the long-term service condition, the mooring line of the deep-water floating platform may fail due to various reasons, such as overloading caused by an accidental condition or performance deterioration. Therefore, the safety performance under the transient responses process should be evaluated in advance, during the design phase. A series of time-domain numerical simulations for evaluating the performance changes of a Floating Production Storage and Offloading (FPSO) with different broken modes of mooring lines was carried out. The broken conditions include the single mooring line or two mooring lines failure under ipsilateral, opposite, and adjacent sides. The resulting transient and following steady-state responses of the vessel and the mooring line tensions were analyzed, and the corresponding influence mechanism was investigated. The accidental failure of a single or two mooring lines changes the watch circle of the vessel and the tension redistribution of the remaining mooring lines. The results indicated that the failure of mooring lines mainly influences the responses of sway, surge, and yaw, and the change rule is closely related to the stiffness and symmetry of the mooring system. The simulation results could give a profound understanding of the transient-effects influence process of mooring line failure, and the suggestions are given to account for the transient effects in the design of the mooring system.

Mathematical modelling to industrial repair and maintenance policy system for its reliability

The present paper is an initiative taken by emerging reliability model to a automobile repair industries for its products by dividing repair policy into two categories as (a) regular/normal service and (b) strategy for accidental or additional failure. The concept of inspection process has been introduced for proper verification of failure and also to its repairing strategy with time and cost. The maintenance cost for regular services are fixed but for the case of additional failures the additional cost will be decided upon the level of damage. The stochastic analysis for system been numerically and graphically analyzed by calculating reliability variables like MTSF, availability, inspection and maintenance analysis of the system with the concept of geometric distribution, Markov process and regenerative technique. The results been proved beneficial for fulfilling the objective of calculating profit function that increases with increasing repair and decreasing failure rate.

Improving the properties of wheeled steel during thermal repair

The purpose: to increase durability and life of railway wheels and to reduce the cost of purchasing new ones by restoring the mechanical properties of the metal rim and improving its structure. Methods: study using a multiple electron microscope and local X-ray spectral analysis of wheeled steel after induction thermocyclic processing at a high-frequency facility and in a state of delivery. Results: The structure resulting from induction thermocyclic processing - sorbit leads to the formation of compressive stresses, which has a positive effect on the efficiency of the surface of the wheel. As a result, the reliability of the wheel on accidental failures (cranks, chippings, etc.) is improved and, as a result, the safety of the operation of rolling stock is improved. Practical importance: the rational use of induction wheel heating technology will improve the efficiency of the use of rolling stock by significantly reducing the number of purchases of new wheel pairs.

Examination of mercury contamination from a recent coal ash spill into the Dan River, North Carolina, United States

Coal ash spills occasionally occur due to the accidental failure of surface impoundments, and toxic metal-laden ash can pose a serious health threat to adjacent aquatic ecosystems. Here, we performed an investigation into longitudinal variations of mercury (Hg) contamination in the Dan River (North Carolina, United States) about 17 and 29 months after a February 2014 coal ash spill incident, in which the reported Hg concentrations in the spilled coal ash (210 ng/g) were 1–2 orders of magnitude higher than the river sediments (2–61 ng/g). We examined total Hg (THg) and methyl Hg (MeHg) in sediments from 0 to 65 km downstream of the spill, and found that most of the variations of THg and MeHg in surface sediments (0–16 cm) could be well accounted by the organic matter content and appeared to be not contaminated by Hg derived from coal ash. In examining MeHg bioaccumulation in invertebrates (aquatic and riparian) and fish in the Dan River and fish in a reservoir downstream of Dan River, we found no evidence of elevated MeHg bioaccumulation due to the 2014 coal ash spill. Thus, we concluded that Hg contamination from the coal ash spill is largely absent in the Dan River for both surface sediments and biota within the first three years of spill (until 2017), even though the majority of coal ash may be buried deeper in the sediment in the river channel and/or the downstream reservoir. Alternatively, the Hg associated with the coal ash is largely not bioavailable for extensive microbial Hg methylation. The findings provide useful insights into remediation strategies for this incident and other coal ash spills.

Progressive Collapse of flat slab structures – key elements and connections

The loss of even one vertical support member can lead to catastrophic consequences and the progressive collapse of big portion or even the entire structure of the building. This report presents a computational study of a single-story, non-scaled 3D fragment of a high-rise concrete flat slab structure building with peripheral beams along the facade in case of dynamic failure of a column. The main objective is to examine alternative load paths for the transfer of stress from the peripheral beams to the columns, across the slab and its punching areas. In case of accidental failure of an outer column, the facade beams serve as prevention which reduces the redistribution of loads to the interior, ie. to the columns with critical slab punching areas. Research on the performance of peripheral beams and the key role of corner columns is the focus of this report.

An opportunistic maintenance policy for offshore wind farms

An opportunistic maintenance policy for offshore wind farms is introduced, considering imperfect maintenance and the weather window effect. Each wind turbine is regarded as a multi-component system divided into several assemblies. When one unit fails or reaches its critical degradation state, there is an opportunity to implement preventive maintenance for the others, reducing the losses of accidental failures. On the basis of the rolling horizon approach, the system condition is updated after the completion of a maintenance activity. By selecting the optimized maintenance combination at every opportunity, the maintenance plan over the mission period is finalized. The uncertainty of maintenance effectiveness and the costs of the time waiting for a weather window are also considered. Failure information is collected from existing literature to accomplish the calculations. Calculated results indicate that the proposed approach is beneficial to save the maintenance expenditure of offshore wind farms.

Structural response analysis of the hydraulic pneumatic tensioner under its local failure based on a fully coupled TLP-TTR system

The presented work studied the structural response of the hydraulic pneumatic tensioner (HPT) in a TLP-TTR system with failure of the tensioner cylinder. A fully coupled hull-tendon-TTR-tensioner model was established in AQWA to simulate the failure numerically. A specific HPT was modeled by considering 4 cylinders and the real-time stroke of each piston. A set of formulas was proposed to calculate the real-time tension including different components, e.g. Stribeck friction, in the tensioner. A riser array including 6 independent production TTRs and their tensioners was also modeled. The production TTR model was stacked up by different specific riser joints. The hydrodynamic force acting on the hull was obtained by using the 3D potential flow theory. The real-time tensions on different tensioner cylinders were obtained by using an in-house-developed program. Different environmental conditions, including a calm sea, regular waves, and extreme sea states, were considered in the simulations. In the results, the behaviors of different cylinders of the failed tensioner were presented. The results show that when an accidental local failure of the HPT occurs, the tension and stroke responses are still far from the designed-limits to induce a progressive failure.

Experimental and theoretical study of seismic and progressive collapse resilient composite frames

A steel-concrete composite frame is typically used for building construction. Earthquake action and progressive collapse event caused by accidental local failures are the primary threats affecting the safety of steel-concrete composite frames. Currently, multi-hazard resistance and building resilience have garnered much research attention from the international civil engineering community. Based on the previously proposed first-generation seismic and progressive collapse resistant composite frame (SPCRCF), an improved second-generation seismic and progressive collapse resilient steel-concrete composite frame (SPCRCF-2) is proposed. The performance of SPCRCF-2 is compared with that of SPCRCF as well as a conventional steel-concrete composite frame (CSCCF) through seismic and progressive collapse experiments. Compared with CSCCF and SPCRCF, SPCRCF-2 is proven to be able to localize the damage to the replaceable energy-dissipating (ED) components under both seismic and progressive collapse conditions, whilst maintaining the other key components (beams and columns) damage-free. This special feature facilitates rapid repair of the structure thereby achieving multi-hazard resilience. Finally, theoretical models are proposed to calculate the initial stiffness and flexural yield strength of the beam-column joint connection in SPCRCF-2. The models are further validated by the experimental results.

A Novel End-To-End Fault Diagnosis Approach for Rolling Bearings by Integrating Wavelet Packet Transform into Convolutional Neural Network Structures.

Accidental failures of rotating machinery components such as rolling bearings may trigger the sudden breakdown of the whole manufacturing system, thus, fault diagnosis is vital in industry to avoid these massive economical costs and casualties. Since convolutional neural networks (CNN) are poor in extracting reliable features from original signal data, the time-frequency analysis method is usually called for to transform 1D signal into a 2D time-frequency coefficient matrix in which richer information could be exposed more easily. However, realistic fault diagnosis applications face a dilemma in that signal time-frequency analysis and fault classification cannot be implemented together, which means manual signal conversion work is also needed, which reduces the integrity and robustness of the fault diagnosis method. In this paper, a novel network named WPT-CNN is proposed for end-to-end intelligent fault diagnosis of rolling bearings. WPT-CNN creatively uses the standard deep neural network structure to realize the wavelet packet transform (WPT) time-frequency analysis function, which seamlessly integrates fault diagnosis domain knowledge into deep learning algorithms. The overall network architecture can be trained with gradient descent backpropagation algorithms, indicating that the time-frequency analysis module of WPT-CNN is also able to learn the dataset characteristics, adaptively representing signal information in the most suitable way. Two experimental rolling bearing fault datasets were used to validate the proposed method. Testing results showed that WPT-CNN obtained the testing accuracies of 99.73% and 99.89%, respectively, in two datasets, which exhibited a better and more reliable diagnosis performance than any other existing deep learning and machine learning methods.

절삭 제동을 통한 추락 방지용 고속 안전 브레이크 설계

Free fall safety brakes against accidental cable failure such as in elevators may require friction, wedging action, eddy current, and other effects. An ideal safety brake system should be quick in its deployment with sufficient payload capacity in compact dimensions. In this study, a safety braking system with a quick deployment mechanism is proposed. The mechanism housed in a carrier is suspended by the cable and connected to the payload. At the onset of cable failure, a linkage system is driven by a pre-loaded spring to drive terminal cutting tools tips against the sacrificial braking pads on each side of the vertical track. Experiments showed that large braking force may be achieved by a compact mechanism. Several design issues of linkage deployment, braking force control, and drop dynamics are discussed.

Decentralized-distributed robust electric power scheduling for multi-microgrid systems

This paper proposes a novel decentralized-distributed (DD) adaptive robust optimization (ARO) method to address the efficient distributed scheduling of multi-microgrid systems involving various entities, uncertainties and accidental communication failures. To avoid an unavailable coordination center of the whole network, a DD-ARO model is firstly proposed based on the parallelizing-distributed (PD) framework, which allocates the task of tie-line power coordination in the virtual center to the neighboring stakeholders. According to the properties of nonlinear ARO, a modified analytical target cascading method is further developed to formulate the consistency constraints on shared tie-lines, thus guaranteeing the optimality and enhancing the solution quality of the DD-ARO model. Finally, an iterative solution algorithm is proposed to efficiently solve the resulting multi-level non-convex DD-ARO model. Case studies and computational results illustrate the effectiveness of the DD-ARO approach for an AC/DC hybrid multi-microgrid system under normal and faulty communications.

Estimating traffic change in accidental regional node failure for Asia pacific IP networks

Connectivity seems to be one of the significant features of today’s life. People rely on their technology in almost every aspect of their daily living. They also depend on this technology to be accessible anytime and anywhere. It is true that technology has touched every feature of today’s life. However, it is the networks that allowed this touch to reach almost everyone, regardless of who or where they are. Disasters stand for the oldest challenges that ever faced humanity. Since societies are extremely dependent on the technology, it is imperative to face the challenge in terms of technological communication systems. In this paper, the Accidental Disaster Network Impact Model is used to study the impact of a regional computer network failure triggered by an accidental disaster on the surviving network. The main aim is to study the percentage of change in traffic and lost traffic in node failure scenarios. This research estimates the change in traffic in cases of single node failure and double node failure. Also, it addresses the case of partial node failure in which only part of the communication ability is lost. The research also generates a simplified network map that represents the regional network of Asia Pacific.

Coordination strategy between AFS and ASB with fault-tolerant mechanism for ground vehicle

In order to improve the performance of ground vehicle equipped with the active front-wheel steering and active stabilizer bar, the coordination for the two systems has been researched. A layered functional framework is proposed: the upper controller coordinates yaw motion with a designed Fuzzy proportional–integral–derivative controller algorithm correcting the outputs of active front-wheel steering and active stabilizer bar; for the middle subsystems, an ideal steering ratio is designed with the Sigmoid function to achieve the active steering, and a sliding mode algorithm is designed to reduce the roll angle; the bottom actuators achieve the control target from the middle layer. In addition, the upper layer has a rebuilt fuzzy rule-based fault-tolerant mechanism that handles the failure of stabilizer bar actuators to guarantee the stability of roll and yaw motion. Finally, the simulation and rapid-control-prototype test for step steering show that the designed algorithm can ensure roll and yaw performance. In consideration of the accidental failure of active stabilizer bar actuators, by actively adjusting the coordinated rules, the system could overcome the contradiction of coupling control and still maintain yaw and roll stability, which improves the active safety.

A Novel Interpolation-SVT Approach for Recovering Missing Low-Rank Air Quality Data

With increasing public demands for timely and accurate air pollution reporting, more air quality monitoring stations have been deployed by the governments in urban metropolises to increase the coverage of urban air pollution monitoring. However, due to systematic or accidental failures, some air pollution measurements obtained from these stations are found to have missing values, which will adversely affect the accuracy of any follow-up air pollution analyses and the quality of environmental decision-makings. In this study, the mathematical property of air quality measurements is investigated to recover the missing air pollution values. A new algorithm, which matches meteorology data with air pollution data from different locations, to reconstruct the data matrix and recover missing entries, is proposed. Next, a Low Rank Matrix Completion problem is used to reconstruct the missing values, by transforming the data recovery problem to a sub-gradient primal-dual problem, based on the duality theory, with Singular Value Thresholding (SVT) employed to develop sub-optimal solutions. Next, an Interpolation-SVT (ISVT) approach is adopted to handle the sparsity of observed measurements. Comprehensive case studies are conducted to evaluate the performance of the proposed methods. The simulation results have demonstrated that the proposed SVT and ISVT methods can effectively recover the missing air pollution data and outperform existing interpolation methods and data imputation techniques. The proposed study can improve air pollution estimation and prediction whenever the low-rank data types that are used as proxies for air pollution estimation contain a lot of missing values and require data recovery.

The method of software reliability increasing for the microprocessors with multi-byte command system

The article considers an original way of software reliability improvement of microprocessor systems with multi-byte command system in case of errors due to accidental failure while execution of the program. Program running errors (control flow errors) mean a discrepancy in the sequence of command codes executed by the microprocessor after the failure occurrence, with the working sequence of commands. The method is based on the preliminary marking of the program memory codes with the help of an additional parity/odd bit and the formation of the signal of the command code reading by microprocessor when accessing the program memory. The article proposes the analytical relations to predict the probability of detection of control flow errors for CISC-processors with any multibyte system of commands based on statistics of commands of different byteness which is contained in the code of the executable program. Along with the detection of control flow errors, all odd errors are also detected while reading the content of any program memory cell.

A self-healing silicone/BN composite with efficient healing property and improved thermal conductivities

Polymer dielectric composites with excellent thermal conductivity have received increasing attention in the modern electronics industry due to their outstanding thermal management performance. However, conventional polymers used for the thermally conductive composites usually suffer from accidental mechanical failure, causing decrease in service life or loss of functionality. In this work, we prepared a self-healing silicone/BN composite simultaneous with high thermal conductivity, high self-healing efficiency and low electrical conductivity. Silicone cross-linked by DA adduct was used as polymer matrix and BN was used as thermally conductive filler. The self-healing silicone/BN composite exhibited a high self-healing efficiency of higher than 90% and an enhancement of 544% in thermal conductivity at BN content of 50 wt%. The self-healing composites presented excellent thermal management performance. The excellent self-healing properties were attributed to the thermal reversibility of the DA reaction and the flexibility of the siloxane molecules. In addition, the self-healing silicone/BN composite with 50 wt% of BN exhibited a low dielectric dissipation factor of 0.017 and an enhancement of 568% in tensile strength.

Default contagion and systemic risk in loan guarantee networks

AbstractThis paper studies systemic risk in the Chinese debt market stemming from inter‐corporate loan guarantees using field data from Zhejiang Province. We apply a weighted and directed network model to analyse the implications for default contagion and systemic risk under different stress testing scenarios. The empirical results indicate that the topology of the loan guarantee network is close to a ‘scale‐free’ structure, which is known to be robust against accidental failures but vulnerable to coordinated attacks. Hence, the network is able to cope with idiosyncratic shocks resulting from single company failures, but can easily suffer from more widespread contagion if a group of systemically important companies are hit by a targeted shock. We further demonstrate that within our sample of small and medium‐sized enterprise (SME) companies, increasing leverage reduces network stability and exacerbates the effects of contagion. More lenient bank lending policies increase the survival rate of sample companies and thereby reduce the losses from default contagion.

Conceptualizing the key features of cyber‐physical systems in a multi‐layered representation for safety and security analysis

AbstractMany safety‐related systems are evolving into cyber‐physical systems (CPSs), integrating information technologies in their control architectures and modifying the interactions among automation and human operators. Particularly, a promising potential exists for enhanced efficiency and safety in applications such as autonomous transportation systems, control systems in critical infrastructures, smart manufacturing and process plants, robotics, and smart medical devices, among others. However, the modern features of CPSs are ambiguous for system designers and risk analysts, especially considering the role of humans and the interactions between safety and security. The sources of safety risks are not restricted to accidental failures and errors anymore. Indeed, cybersecurity attacks can now cascade into safety risks leading to physical harm to the system and its environment. These new challenges demand system engineers and risk analysts to understand the security vulnerabilities existing in CPS features and their dependencies with physical processes. Therefore, this paper (a) examines the key features of CPSs and their relation with other system types; (b) defines the dependencies between levels of automation and human roles in CPSs from a systems engineering perspective; and (c) applies systems thinking to describe a multi‐layered diagrammatic representation of CPSs for combined safety and security risk analysis, demonstrating an application in the maritime sector to analyze an autonomous surface vehicle.

Structural and health assessment of historic timber roofs from the Convent of Christ in Tomar

Before coming up with any important decision of intervention in the restoration process of existing buildings, the assessment of the conservation state is required as regards heritage timber structures and especially for those that suffered a lack of maintenance in their service life. In that context, three timber roof structures from the Convent of Christ in Tomar, Portugal, were selected and investigated. To this end, a research methodology was introduced and applied to these case studies into four main steps: (1) visual inspection; (2) non-destructive wood diagnosis; (3) structural safety evaluation; (4) prevention and intervention measures. For the visual inspection, every element and joint constituting the roof structures received scrutiny through assessing the wood species, the different construction stages and, last but not least, their respective geometry. As regards the encountered pathologies, structural disorders (e.g. accidental failure, serviceability defects…) and wood deteriorations due to biological agents (e.g. wood-destroying fungi or insects), which ineluctably leads to a likely decrease of the mechanical performances of the roof structure, were reported. To estimate the residual element cross section and elastic modulus, wood diagnosis was carried out using three relevant non-destructive tests: (1) ultrasonic pulse velocity; (2) drilling resistance; (3) impact penetration. From the collected data, the three timber roof structures were modelled on a commercial software to check their safety and integrity. Based on those outcomes, some prevention and intervention measures haves been lastly proposed case by case.