Unknown Failure Research Articles

연천댐 사례를 통한 댐 파괴 부정류해석 및 하류 영향 검토(II) -시나리오에 따른 댐 하류 부정류 해석 및 범랑특성 연구-

This study aims at the analyze of unsteady downstream flow due to dam failure along dam failure scenario and applied to Yeoncheon Dam which was collapsed August 1st 1999, using HEC-RAS simulation model. The boundary conditions of this unsteady flow simulation are that dam failure arrival time could be at 02:45 a.m. August 1st 1999 and failure duration time could be also 30 minutes. Downstream 19.5 km from dam site was simulated for unsteady flow analysis in terms of dam failure and non-failure cases. For the parameter calibration, observed data of Jeonkok station were used and roughness coefficient was applied to simulation model. The result of the peak discharge difference was 2,696 to <TEX>$1,745\;m^3/sec$</TEX> along the downstream between dam failure and non-failure and also peak elevation of water level showed meanly 0.6m difference. Those results of these studies show that dam failure scenarios for the unknown failure time and duration were rational because most results were coincident with observed records. And also those results and procedure could suggest how and when dam failure occurs and downstream unsteady flow analyzes.

Packaging influences on the reliability of MEMS resonators

In this paper, the effect of assembly processes on the reliability of MEMS resonators is investigated. The common functions of MEMS resonators in the current technology are described as well as the most common designs. Virtual prototyping of a resonator during several assembly steps is used to estimate their influence. Experiments are executed in order to verify the simulation results. These experiments are also used to find yet unknown failure modes.

Non-parametric estimation of the availability in a general repairable system

This work deals with repairable systems with unknown failure and repair time distributions. We focus on the estimation of the instantaneous availability, that is, the probability that the system is functioning at a given time, which we consider as the most significant measure for evaluating the effectiveness of a repairable system. The estimation of the availability function is not, in general, an easy task, i.e., analytical techniques are difficult to apply. We propose a smooth estimation of the availability based on kernel estimator of the cumulative distribution functions (CDF) of the failure and repair times, for which the bandwidth parameters are obtained by bootstrap procedures. The consistency properties of the availability estimator are established by using techniques based on the Laplace transform.

Late prosthetic valve endocarditis due to &lt;i&gt; Cardiobacterium hominis,&lt;/i&gt; an unusual complication

We report a case of prosthetic valve endocarditis caused by Cardiobacterium hominis in a patient who had undergone atrial septal defect closure and mitral valve replacement of the heart in 1978. He presented with pyrexia of unknown origin and congestive cardiac failure. Investigations revealed infective endocarditis of prosthetic valve in mitral portion. Blood culture samples grew C. hominis. The patient was empirically started on vancomycin and gentamicin intravenously and ceftriaxone was added after isolation of the organism. Though subsequent blood cultures were negative, patient remained in congestive cardiac failure and died due to complications.

Cellular Automata Model for Predicting the Failure Pattern of Laterally Loaded Masonry Wall Panels

This paper introduces a technique that directly predicts the failure patterns of laterally loaded masonry panels based on the results of existing typical panels tested in the laboratory. The technique is based on the use of the cellular automata (CA). In this technique, the CA modeling is established to propagate boundary effects to zones within a panel. The corresponding rules for the state values of zones are derived from the proposed CA model, using appropriate transition functions. These state values are then used by the CA to establish zone similarity between two panels. Finally, the zone similarity is applied to establish locations of cracks on the panel. The technique is used in a novel way that eliminates the use of any numerical tools such as finite-element analysis (FEA). This technique is purely based on comparing the failure pattern of the base panel (a panel whose failure pattern is known from the laboratory tests) and unseen panels (panels not tested in the laboratory by the writers or with unknown failure patterns) subjected to the same type of loading and with similar boundary conditions to predict the failure load of the unseen panels.

Experimental study of surface crystallization on integrated circuit chips

A surface crystallization phenomenon on bonding pads and wires of integrated circuit chip is reported in this paper. Through a lot of experiments, an unknown failure effect caused by mixed crystalline matter is revealed, whereas non-plasma fluorine contamination cannot cause the failure of bonding pads. By experiments combined with infrared spectroscopy analysis, the surface crystallization effect is studied. The conclusion of the study can provide the guidance for IC fabrication, modelling and analysis.

Medulloblastoma with extracentral nervous system metastases: clinical presentation and risk factors

Purpose Extra-central nervous system (extra-CNS) metastases are relatively unknown failure patterns in medulloblastoma. The aim of this study was to analyse epidemiological, clinical and aetiopathological aspects of these extra-CNS localisations. Patients and methods Extra-CNS metastases were retrospectively identified in patients treated in the department of radiation therapy at Salah-Azaïz institute (ISA) for medulloblastoma. These metastases were diagnosed as extra-CNS for all secondary localisations not related to other tumour aetiology. Aetiopathological aspects are discussed with a literature review. Results Among 103 patients treated and followed-up in the department of radiation therapy of ISA from 1970 to 1992, 8 developed extra-CNS metastases (7.7%). Age at diagnosis of primitive tumour varied from 3 to 23 years. Sex ratio was 1. Primitive tumour treatment was: complete surgical resection in 4 patients with preoperative cerebrospinal fluid shunting in two, cerebrospinal axis irradiation in 7 patients and a cerebral-limited irradiation in 1. Two patients received chemotherapy for their initial treatment (systemic in one case and intrathecal in the other). The mean free-interval from diagnosis of primitive tumour to extra-CNS metastases was 23 months, varying from 8 to 53 months. These metastases were located in the liver (1 case), cervical lymph nodes (2 cases), bone marrow (1 case) and bone (2 cases). Two patients had multiple metastases: bone and bone marrow (in one), lung, pleura, cervical lymph node and bone localisations (in one). Treatment of these metastases was: chemotherapy in 5 cases, chemotherapy and radiation in one, radiation therapy in one and 2 patients were given only supportive care treatment. All patients died or are in progressive disease in less than one year from the diagnosis of extra-CNS metastases. Conclusion Extra-CNS metastases are not rare and have a poor prognosis. The most commonly involved sites are bone, cervical lymph nodes and bone marrow. A complete work-up at initial diagnosis is recommended to screen early metastases. Literature review showed that histopathologic grading might help to identify groups at risk.

Adaptive output feedback actuator failure compensation for a class of non‐linear systems

AbstractAn adaptive compensation control scheme using output feedback is designed and analysed for a class of non‐linear systems with state‐dependent non‐linearities in the presence of unknown actuator failures. For a linearly parameterized model of actuator failures with unknown failure values, time instants and pattern, a robust backstepping‐based adaptive non‐linear controller is employed to handle the system failure, parameter and dynamics uncertainties. Robust adaptive parameter update laws are derived to ensure closed‐loop signal boundedness and small tracking errors, in general, and asymptotic regulation, in particular. An application to controlling the angle of attack of a non‐linear hypersonic aircraft dynamic model in the presence of elevator segment failures is studied and simulation results show that the developed adaptive control scheme has desired actuator failure compensation performance. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Intelligent on-line fault tolerant control for unanticipated catastrophic failures

As dynamic systems become increasingly complex, experience rapidly changing environments, and encounter a greater variety of unexpected component failures, solving the control problems of such systems is a grand challenge for control engineers. Traditional control design techniques are not adequate to cope with these systems, which may suffer from unanticipated dynamic failures. In this research work, we investigate the on-line fault tolerant control problem and propose an intelligent on-line control strategy to handle the desired trajectories tracking problem for systems suffering from various unanticipated catastrophic faults. Through theoretical analysis, the sufficient condition of system stability has been derived and two different on-line control laws have been developed. The approach of the proposed intelligent control strategy is to continuously monitor the system performance and identify what the system's current state is by using a fault detection method based upon our best knowledge of the nominal system and nominal controller. Once a fault is detected, the proposed intelligent controller will adjust its control signal to compensate for the unknown system failure dynamics by using an artificial neural network as an on-line estimator to approximate the unexpected and unknown failure dynamics. The first control law is derived directly from the Lyapunov stability theory, while the second control law is derived based upon the discrete-time sliding mode control technique. Both control laws have been implemented in a variety of failure scenarios to validate the proposed intelligent control scheme. The simulation results, including a three-tank benchmark problem, comply with theoretical analysis and demonstrate a significant improvement in trajectory following performance based upon the proposed intelligent control strategy.

Reconfigurable control system design for fault diagnosis and accommodation.

The growing demand in system reliability and survivability under failures has urged ever-increasing research effort on the development of fault diagnosis and accommodation. In this paper, the on-line fault tolerant control problem for dynamic systems under unanticipated failures is investigated from a realistic point of view without any specific assumption on the type of system dynamical structure or failure scenarios. The sufficient conditions for system on-line stability under catastrophic failures have been derived using the discrete-time Lyapunov stability theory. Based upon the existing control theory and the modern computational intelligence techniques, an on-line fault accommodation control strategy is proposed to deal with the desired trajectory-tracking problems for systems suffering from various unknown and unanticipated catastrophic component failures. Theoretical analysis indicates that the control problem of interest can be solved on-line without a complete realization of the unknown failure dynamics provided an on-line estimator satisfies certain conditions. Through the on-line estimator, effective control signals to accommodate the dynamic failures can be computed using only the partially available information of the faults. Several on-line simulation studies have been presented to demonstrate the effectiveness of the proposed strategy. To investigate the feasibility of using the developed technique for unanticipated fault accommodation in hardware under the real-time environment, an on-line fault tolerant control test bed has been constructed to validate the proposed technology. Both on-line simulations and the real-time experiment show encouraging results and promising futures of on-line real-time fault tolerant control based solely upon insufficient information of the system dynamics and the failure dynamics.

Reliability prediction models to support conceptual design

During the early stages of conceptual design, the ability to predict reliability is very limited. Without a prototype to test in a lab environment or without field data, component failure rates and system reliability performance are usually unknown. A popular method for early reliability prediction is to develop a computer model for the system. However, most of these models are extremely specific to an individual system or industry. This paper presents three general procedures (using both simulation and analytic solution techniques) for predicting system reliability and average mission cost. The procedures consider both known and unknown failure rates and component-level and subsystem-level analyzes. The estimates are based on the number of series subsystems and redundant (active or stand-by) components for each subsystem. The result is a set of approaches that engineers can use to predict system reliability early in the system-design process. Software was developed (and is discussed in this paper) that facilitates the application of the simulation-based techniques. For the specific type of system and mission addressed in this paper, the analytic approach is superior to the simulation-based prediction models. However, all three approaches are presented for two reasons: (1) to convey the development process involved with building these prediction tools; and (2) the simulation-based approaches are of greater value as the research is extended to consider more complex systems and scenarios.

Automated hazard analysis of digital control systems

Digital instrumentation and control (I&C) systems can provide important benefits in many safety-critical applications, but they can also introduce potential new failure modes that can affect safety. Unlike electro-mechanical systems, whose failure modes are fairly well understood and which can often be built to fail in a particular way, software errors are very unpredictable. There is virtually no nontrivial software that will function as expected under all conditions. Consequently, there is a great deal of concern about whether there is a sufficient basis on which to resolve questions about safety. In this paper, an approach for validating the safety requirements of digital I&C systems is developed which uses the Dynamic Flowgraph Methodology to conduct automated hazard analyses. The prime implicants of these analyses can be used to identify unknown system hazards, prioritize the disposition of known system hazards, and guide lower-level design decisions to either eliminate or mitigate known hazards. In a case study involving a space-based reactor control system, the method succeeded in identifying an unknown failure mechanism.

AN ADAPTIVE CONTROL SCHEME FOR OUTPUT FEEDBACK NONLINEAR SYSTEMS WITH ACTUATOR FAILURES

An adaptive control scheme to achieve stability and output tracking is presented for the output-feedback nonlinear plant with unknown actuator failures. A state observer is designed for estimating the unavailable plant states, based on a chosen control strategy, in the presence of actuator failures with unknown failure values, time instants and pattern. An adaptive controller is developed by employing the backstepping technique, for which parameter update laws are derived to ensure asymptotic output tracking and signal boundedness of the closed-loop system, as shown by detailed stability analysis.

Investigation of Burn-in problems with unknown failure time distribution

The determination of the optimal burn-in-time is related with the minimization of the expected costs of the manufacturing and/or the warranty. We derive solutions that are based on the use of estimators which are functions of the estimated density function. They are consistent.

Bayesian maintenance policies during a warranty period

Most of the brand new items are released on the market with a certain type of warranty. A fixed length warranty period is assumed in this paper. A set of maintenance policies which consist of minimal repair and preventive maintenance is analyzed for the case of known and unknown failure parameters of the item's lifetime distribution. For the second case, two types of Bayesian policies are considered. An extensive simulation study comparing the performance of these maintenance policies is performed

Failure modes of LV overhead insulated mains

A survey of operating problems and failure mechanisms on LV aerial bundled cables is presented. Previously unknown failure modes are identified and new test procedures are given. The influence of moisture ingress, corrosion, wind, flora, fauna, weathering and overloads is identified and discussed.

Draught and vertical forces obtained from dynamic soil cutting by plane tillage tools

An understanding of the relationship between tool forces and speed is important in evolving management strategies for optimum performance. The effect of speed on tillage tool forces were studied experimentally for wide (width=25.4 cm, depth=15 cm) and narrow (width=5.1 cm, depth=22.9 cm) plane tillage blades operating in a Dystric Fluvisol (silty sand texture) in a soil bin. The tools were tested at two depths (10 cm and 15 cm for wide blade, 11.4 cm and 22.9 cm for narrow blade), two rake angles (45° and 90°) and eight speed levels (0.25, 0.5, 0.75, 1.00, 1.25, 1.50, 1.75 and 2.00 m/s). The variables were combined in a 2×2×8 factorial experiment with three replications. The performance of three theoretical models based on the trial wedge approach in predicting the experimental results was evaluated. The first model (Model 1), based on Soehne's approach (with modification for the three-dimensional analysis) assumes that the soil fails in a series of shear planes, forming a wedge that is trapezoidal in shape. The equilibrium of the wedge boundary forces produce the force required for failure. The second model (Model 2), based on Mckyes' approach assumes that soil failure is by the formation of a centre wedge flanked by two side crescents. Equilibrium of the boundary forces on the wedge and crescents produce the forces as a function of an unknown failure angle which is obtained by minimizing the weight component of the total force. Model 3, based on Perumpral's approach assumes the same failure wedge as Model 2 but the total cutting force is minimized instead. Experimental results show that the tool force (draught and vertical force) is a function of the speed and the square of speed whereas the three models assume it to be a function of the square of speed only. The models were not very accurate in predicting the experimental results. The average percent deviation of the predicted forces from the observed values were 43%, 40% and 66% for Models 1, 2 and 3, respectively. Thus, Model 2 had more general agreement with experimental observations. The models were better in predicting the forces (draught and vertical force) for the narrow tool with average percent deviations of 33%, 28% and 46% for Models 1, 2 and 3, respectively, as compared to 53%, 51% and 85% for the wide blade.

Estimation of Weibull distribution parameters for irregular interval group failure data with unknown failure times

Summary This paper presents three methods for estimating Weibull distribution parameters for the case of irregular interval group failure data with unknown failure times. The methods are based on the concepts of the piecewise linear distribution function (PLDF), an average interval failure rate (AIFR) and sequential updating of the distribution function (SUDF), and use an analytical approach similar to that of Ackoff and Sasieni for regular interval group data. Results from a large number of simulated case problems generated with specified values of Weibull distribution parameters have been presented, which clearly indicate that the SUDF method produces near-perfect parameter estimates for all types of failure pattern. The performances of the PLDF and AIFR methods have been evaluated by goodness-of-fit testing and statistical confidence limits on the shape parameter. It has been found that, while the PLDF method produces acceptable parameter estimates, the AIFR method may fail for low and high shape parameter values that represent the cases of random and wear-out types of failure. A real-life application of the proposed methods is also presented, by analyzing failures of hydrogen make-up compressor valves in a petroleum refinery.

Approximate confidence intervals after a sequential clinical trial comparing two exponential survival curves with censoring

A sequential test is considered for comparing two exponential survival curves with unknown failure rates θ 1, θ 2 > 0. The survival times are censored by both real time and an independent censoring variable. It is shown how very weak expansions for the bivariate version of the signed root transformation may be used to construct an approximate confidence interval for δ = log( θ 1 θ 2 ) following the test. The accuracy of the method is illustrated by simulation results for several sequential tests and data-dependent allocation rules.

Designing Component Test Plans for Series System Reliability via Mathematical Programming

For verification of system reliability it is often necessary to conduct individual tests of components that compose the system. We consider a series system consisting of components with unequal test costs and unknown constant failure rates with preassigned bounds on the latter. We derive minimum costcomponent test plans that guarantee specified values of producers' and consumers' risks on the system reliability. These plans are derived for the case in which the component failure times are exponentially distributed, as well as the case in which they follow a gamma distribution. The optimization problems are formulated and solved via standard mathematical programming techniques.