Mass failures are often induced or activated by the variation of hydrological factors within a reservoir area. Clarifying the relationships between the failure volume and different hydrological ...factors may help to identify both the dominant factors influencing reservoir bank failures and the most hazardous combinations of factors inducing such events. This study examines the influence of different hydrological factors on bank failures using model experiments incorporating variations in rainfall, wave and water level. The results indicate that the coupled effects of heavy rainfall and falling water‐level had the most significant impact on bank failure. The cumulative failure mass of the reservoir bank peaked at 177.2 × 103 cm3 under the coupled effects of rainfall and falling water‐level. In comparison, the cumulative mass failures on the reservoir bank under rainfall superimposed onto waves and rainfall superimposed onto water level rise were 162.4 × 103 and 129.2 × 103 cm3, respectively. The impact of heavy rainfall significantly contributed the mass failures on soil reservoir bank. The analysis reveals that the highest cumulative failure, 106.3 × 103 cm3, occurred during periods of heavy rainfall. Compared with heavy rainfall, the cumulative failure volumes in the reservoir experienced a reduction of 46% and 55% under solely declining and solely rising reservoir water levels, respectively. The early phases of changing hydrological conditions have a significant effect on the stability of the soil reservoir bank. Mass failures on the bank predominantly occurred during the initial three events of the five simulation experiments performed for each landform, which could account for up to 87% of the total volume. Hence, it is advisable to avoid lowering reservoir water levels during periods of sustained heavy rainfall in order to mitigate the risk of bank failure.
This paper examines the influences of different hydrological factors on soil bank failures in the middle reaches of the Yellow River using model experiments incorporating the variation of rainfall, wave and water level. The coupled effects of heavy rainfall and falling water level had the most significant impact on bank failures. The study illustrates that the early phases of changing hydrological conditions have an essential effect on the stability of the soil reservoir bank.
Forecasting the time of failure of landslides at slope-scale is a difficult yet important task that can mitigate the effects of slope failures in terms of both human lives and economic losses. Common ...applications include public safety situations, where the risk is represented by dwellings built near active landslides or unstable cut slopes that threaten streets and railways, and open-pit mines, for which accurate warnings are fundamental to safeguard workers and simultaneously avoid unnecessary interruptions of the extraction activities.
The scientific literature is populated by many methods, guidelines and approaches regarding forecasting the time of failure or defining the conditions of imminent collapse. Thus, obtaining a synoptic view of the advantages and limitations of these different methodologies has become difficult. At the same time, innovations in technology have opened new possibilities to the application of such techniques, which are examined here.
This paper discusses and classifies these methods, addressing their respective differences and peculiarities to foster the usage even of less popular methods without overlooking the more scientific aspects and issues of landslide forecasting. Finally, an overview of the future trends and challenges is presented to contribute to the debate around this important topic.
Background
A creatinine-based estimation of the renal function lags behind the onset of disease process. Cystatin C is a new marker for acute kidney injury (AKI). However, data are limited in ...patients with acute-on-chronic liver failure (ACLF). We evaluated serum cystatin C as an early predictor of AKI in patients with ACLF.
Methods
In a prospective observational study, patients with ACLF and normal serum creatinine level were included in the study. Serum cystatin C was analyzed with the development of AKI and the disease outcome.
Result
Forty-seven patients (mean age: 43.26±16.34 years; male:female: 2.35:1) were included in the study. AKI developed in 34% of patients during the hospital stay. Receiver operating characteristic (ROC) curve analysis revealed that the best cutoff for baseline cystatin C was 1.47 mg/L with a sensitivity of 0.94 and specificity of 0.68. The cystatin C ((area under the curve AUC=0.853) performance was better than that of the creatinine (AUC=0.699), Child-Turcotte-Pugh (CTP) (AUC=0.661), and model for end-stage liver disease-sodium (MELD-Na) (AUC=0.641). In the univariate analysis, age, platelet count, creatinine, estimated glomerular filtration rate (eGFR)-modification of diet in renal disease (MDRD), cystatin C, and estimated glomerular filtration rate-serum cystatin C (eGFRcysC) were significantly associated with AKI in ACLF patients. Cystatin C was an independent positive predictor of AKI. Cystatin C was positively correlated with the MELD-Na scores (
r
=0.374 and
p
=0.009).
Conclusion
Our study supports previous studies reporting that serum cystatin C is a better predictor for AKI development compared to serum creatinine. Cystatin C may be used as an early marker for new-onset AKI in hospitalized patients with ACLF.
Cascading failures of relay operations in power systems are inherently linked with the propagation of wide-area power system blackouts. In this paper, we consider a power system cascading failure as ...an indicator matrix encoding: what power system relays operated within a cascading failure inherently capturing the component and the sequence of tripping events. We propose that this matrix may then be used with extended forms of variance-based sensitivity estimators to quantitatively rank how sensitive observed power system cascading failures are to power system variables, considering overall system cascading failures as well as cascading failures grouped by network area and relay types. We demonstrate our proposed method by investigating the sensitivity of cascading failures to relay parameters, system conditions, and fault location using a version of the IEEE 39 bus model modified to include protection relays, wind farms, and tap-changing transformers. Input power system variables included: system operational scenario, disturbance location, relay parameters or thresholds. The Case Studies' results confirm the method's utility by successfully generating relative rankings of input variables' importance with respect to cascading failure propagation. The results also show cascading failures' sensitivity to input variables to be high due to non-linear relationships between input variables and cascading failures.
•An overview of state-of-the-art commutation failure (CF) is provided.•A review of the impact of multi-infeed structure on CF is undertaken.•The advantages and limitations of different CF prevention ...methods are examined.•Suggestions and potentially important future research directions are put forward.
Display omitted
Commutation failure (CF) is the main fault type in high voltage direct current (HVDC) systems with line commutated converters. To mitigate CFs, considerable researches have been done either in modelling or control methods. However, with the operation of more and more large-capacity HVDC projects, the coupling characteristics between HVDC and power grid are more complex. The existing reviews tend to focus only on the CFs of a single HVDC itself. This paper provides a more systematic overview of CFs, covering fifteen specific aspects in six areas, including four types of system structures, such as multi-infeed HVDC, and various types of CFs. The mechanism, discrimination, modeling, and prevention of CFs are reviewed extensively in combination with the latest literature. In particular, the advantages and limits of various CFs prevention methods are analyzed and compared in order to reveal the latest research results. Finally, it points out that the analysis and control of multi-infeed HVDC and hierarchical infeed HVDC, the application of artificial intelligence (AI) technology, the improvement of communication-based on 5G technology, harmonic problems, and control and coordination strategies of new auxiliary equipment are challenges and research directions of HVDC CFs in the future.
Systems' Verification Validation and Testing (VVT) are carried out throughout systems' lifetimes. Notably, quality-cost expended on performing VVT activities and correcting system defects consumes ...about half of the overall engineering cost. Verification, Validation and Testing of Engineered Systems provides a comprehensive compendium of VVT activities and corresponding VVT methods for implementation throughout the entire lifecycle of an engineered system. In addition, the book strives to alleviate the fundamental testing conundrum, namely: What should be tested? How should one test? When should one test? And, when should one stop testing? In other words, how should one select a VVT strategy and how it be optimized? The book is organized in three parts: The first part provides introductory material about systems and VVT concepts. This part presents a comprehensive explanation of the role of VVT in the process of engineered systems (Chapter-1). The second part describes 40 systems' development VVT activities (Chapter-2) and 27 systems' post-development activities (Chapter-3). Corresponding to these activities, this part also describes 17 non-testing systems' VVT methods (Chapter-4) and 33 testing systems' methods (Chapter-5). The third part of the book describes ways to model systems' quality cost, time and risk (Chapter-6), as well as ways to acquire quality data and optimize the VVT strategy in the face of funding, time and other resource limitations as well as different business objectives (Chapter-7). Finally, this part describes the methodology used to validate the quality model along with a case study describing a system's quality improvements (Chapter-8). Fundamentally, this book is written with two categories of audience in mind. The first category is composed of VVT practitioners, including Systems, Test, Production and Maintenance engineers as well as first and second line managers. The second category is composed of students and faculties of Systems, Electrical, Aerospace, Mechanical and Industrial Engineering schools. This book may be fully covered in two to three graduate level semesters; although parts of the book may be covered in one semester. University instructors will most likely use the book to provide engineering students with knowledge about VVT, as well as to give students an introduction to formal modeling and optimization of VVT strategy.
Reliability study of electronic system with the physics-of-failure method has been promoted due to the increase knowledge of electronic failure mechanisms. System failure initiates from independent ...failure mechanisms, have effect on or affect by other failure mechanisms and finally result in system failure. Failure mechanisms in a non-repairable system have many kinds of correlation. One failure mechanism developing to a certain degree will trigger, accelerate or inhibit another or many other failure mechanisms, some kind of failure mechanisms may have the same effect on the failure site, component or system. The destructive effect will be accumulated and result in early failure. This paper presents a reliability evaluation method considering correlativity among failure mechanisms, which includes trigger, acceleration, inhibition, accumulation, and competition. Based on fundamental rule of physics of failure, decoupling methods of these correlations are discussed. With a case, reliability of electronic system is evaluated considering failure mechanism dependence.
•Five types of failure mechanism correlations are described.•Decoupling methods of these correlations are discussed.•A reliability evaluation method considering mechanism dependence is proposed.•Results are quite different to results under failure independence assumption.
•Seven types of bolted steel joints under a central-column-removal scenario are tested.•The behaviour and failure modes of these seven types of connections are presented.•The web cleat connection has ...the best performance to form catenary action.•Tensile capacities of joints after large rotations control catenary action.•The rotation capacities of joints are much higher than the recommended values.
Several structural collapse incidents indicate that failure usually started from beam–column joints when exposed to abnormal loads. If the connections are sufficiently robust and there is adequate axial restraint from adjoining structures, catenary action usually forms and gives rise to alternate load paths whenaffected columns are severely damaged, resulting in large deformations in adjoining beams and slabs. This paper presents seven experimental tests of the performance of common types of bolted steel beam–column joints under a central-column-removal scenario. The joint types including web cleat, top and seat angle, top and seat with web angle (TSWA) (8mm angle), fin plate, flush end plate, extended end plate and TSWA(12mm angle) are studied under the central-column-removal scenario. This study provides the behaviour and failure modes of different connections, including their abilities to deform in catenary mode. The test results indicate that the web cleat connection has the best performance in the development of catenary action, and the flush end plate, fin plate and TSWA connections could also deform in a ductile manner and develop catenary action prior to failure. It is worthy to note that tensile capacities of beam–column joints after undergoing large rotations usually control the failure mode and the formation of catenary action. A new tying resistance expression is proposed to consider the effect of large rotation. If large rotation is not considered in the design stage, the joints with poor rotation capacities would fail to achieve the design tying resistances. The test results also demonstrate that the rotation capacities of beam–column joints based on the experimental results in this study were much higher than the recommended values.
The increasing use of Information Technology (IT) has led to many security and other related failures in the banks and other financial institutions in Bangladesh. In this paper, we investigated the ...factors contributing to the failurein the IT system of the banking industry in Bangladesh. Based on the experts' opinions and weight on the specified evaluating criteria, an empirical test was conducted using a rough set theory to produce a framework for the IT system failure factors. In this study, an extended approach involving the integration of rough set theory based flexible Failure Mode and Effect Analysis (FMEA) and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) has beenapplied to help the managers of the corresponding field to identify the factors responsible for the failure of the IT system in the banking industries and then prioritize them accordingly, for the ease of decision-making.In this research, eleven such failure factors were identified, which were then quantitatively analyzed to facilitate managers in crucial decision-making. It was observed that cyber-attack, database hack risks, server failure, network interruption, broadcast data error, and virus effect were the most significant factors for the failure of the IT system. The framework developed in this research can be utilized to assist in efficient decision-makingin other serviceindustries where IT systems play a key role. To the best of the knowledge, this is the first study thatempirically tested key failure factors of the IT system for the banking sector using an integrated method.
Understanding of the failure mechanism and limit support pressure of a shield tunnel face under seepage condition is important in engineering design and construction. Nine physical model tests, i.e. ...three tests in dry sands, three tests in submerged sands under undrained condition, and three tests under seepage condition were carried out. A rigid plate was set in front of the tunnel face to maintain stability at the initial state. By moving the plate backward from the soil, the displacement and earth pressure curve of the tunnel face was obtained. The earth pressure dropped sharply to a constant value which corresponds to the limit support pressure required to stabilize the tunnel face. The limit pressure was found to increase with the cover-to-diameter ratio in a shallow tunnel, and it turned to be irrelevant to cover-to-diameter ratio in a deep tunnel. The ratio of limit pressure and initial earth pressure decreases with the cover-to-diameter ratio, indicating the effect of soil arching in stabilizing tunnel face stability. Under the same water level condition, the limit pressure of tunnel face with seepage is larger than the one without seepage. The limit support pressure under seepage condition is about 70% of the earth pressure at rest; it is about 50% under undrained condition and is about 15% in dry sand. The flow line around the tunnel face was traced by infused pigment, and the distribution was shown to be irrelevant with water level. The image captured by a HD camera during the test was analyzed by PIV (particle image velocimetry) analysis; the soil particle movements and the distribution of shear strain showed the failure mechanism of tunnel face. The failure mode is a combination of a wedge with slip arc and a prism. Comparing with the failure mode in dry sands and in saturated sands below water table undrained condition, the inclination angle of the wedge block under seepage condition is much smaller.
PDF
