• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.342.2-342
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• 2002

Fault tolerant control algorithm fer heteropolar magnetic bearings are presented. This fault tolerant control utilizes grouping of currents as C-cores in order to isolate magnetic fluxes. Hardware requirements to maintain fault tolerant control are reduced since decoupling chokes are not required in this control scheme. The currents supplied to each pole are redistributed, if some coils (ail suddenly, such that the resultant magnetic forces should remain invariant through coil failure events. (omitted)

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4087-4107
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• 2016

The current cloud computing paradigm is still vulnerable to a significant number of system failures. The increasing demand for fault tolerance and resilience in a cost-effective and device-independent manner is a primary reason for creating an effective means to address system dependability and availability concerns. This paper focuses on online failure prediction for cloud computing systems using system runtime data, which is different from traditional tolerance techniques that require an in-depth knowledge of underlying mechanisms. A 'failure prediction' approach, based on Cloud Theory (CT) and the Hidden Markov Model (HMM), is proposed that extends the HMM by training with CT. In the approach, the parameter ω is defined as the correlations between various indices and failures, taking into account multiple runtime indices in cloud computing systems. Furthermore, the approach uses multiple dimensions to describe failure prediction in detail by extending parameters of the HMM. The likelihood and membership degree computing algorithms in the CT are used, instead of traditional algorithms in HMM, to reduce computing overhead in the model training phase. Finally, the results from simulations show that the proposed approach provides very accurate results at low computational cost. It can obtain an optimal tradeoff between 'failure prediction' performance and computing overhead.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.932-935
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• 2002

In this paper, we introduce new FTL(Flash Translation Layer) driver algorithm that tolerate the power off errors. FTL driver is the software that provide the block device interface to the upper layer software such as file systems or application programs that using the flash memory as a block device interfaced storage. Usually, the flash memory is used as the storage devices of the mobile system due to its low power consumption and small form factor. In mobile system, the state of the power supplement is not stable, because it using the small sized battery that has limited capacity. So, a sudden power off failure can be occurred when we read or write the data on the flash memory. During the write operation, power off failure may introduce the incomplete write operation. Incomplete write operation denotes the inconsistency of the data in flash memory. To provide the stable storage facility with flash memory in mobile system, FTL should provide the fault tolerance against the power off failure. SSR (Simple Sector Remapper) is a fault tolerant FTL driver that provides block device interface and also provides tolerance against power off errors.

• Steel and Composite Structures
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• v.1 no.4
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• pp.411-426
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• 2001

This paper treats the failure analysis of prestressing steel wires with different kinds of localised damage in the form of a surface defect (crack or notch) or as a mechanical action (transverse loads). From the microscopical point of view, the micromechanisms of fracture are shear dimples (associated with localised plasticity) in the case of the transverse loads and cleavage-like (related to a weakest-link fracture micromechanism) in the case of cracked wires. In the notched geometries the microscopic modes of fracture range from the ductile micro-void coalescence to the brittle cleavage, depending on the stress triaxiality in the vicinity of the notch tip. From the macroscopical point of view, fracture criteria are proposed as design criteria in damage tolerance analyses. The transverse load situation is solved by using an upper bound theorem of limit analysis in plasticity. The case of the cracked wire may be treated using fracture criteria in the framework of linear elastic fracture mechanics on the basis of a previous finite element computation of the stress intensity factor in the cracked cylinder. Notched geometries require the use of elastic-plastic fracture mechanics and numerical analysis of the stress-strain state at the failure situation. A fracture criterion is formulated on the basis of the critical value of the effective or equivalent stress in the Von Mises sense.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.599-602
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• 2011

A propulsion controller for one-time flight vehicles should be designed robustly so that it can complete its missions even in case sensor failures. These vehicles improve their fault tolerance by back-up sensors prepared for the failure of major sensors, which raises the total cost. This paper presents the NARX model which substitutes vehicles' velocity sensors, and detects failure of sensor signals by using model based fault detection. The designed NARX model and fault detection algorithm were optimized and installed in TI's TMS320F2812 so that they were linked to HILS instruments in real-time. The designed propulsion controller made the vehicle to have better fault tolerance with fewer sensors and to complete its missions under a lot of complicated failure situations. The controller's applicability was finally confirmed by tests under the HILS environment.

• Journal of The Korean Association For Science Education
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• v.29 no.4
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• pp.414-422
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• 2009

In this study, we investigated the influences of students' motivational characteristics on the processes of learning density concept using a discrepant event. The participants were 642 seventh graders from two middle schools. Tests of failure tolerance, self-efficacy and mastery/performance goal orientation were administered as pretests. A preconception test was also administered. The intervention was the students' individual study of the density concept with a worksheet that was designed to incorporate the major steps of conceptual change learning. The tests of attention, effort and conceptual understanding were administered as post-tests. The responses of 203 students who had been found to possess the target misconception were analyzed. The results of a path analysis revealed that students' motivational characteristics variables did not influence cognitive conflict. Failure tolerance and mastery goal orientation, however, influenced conceptual understanding via situational interest, attention and effort. Self-efficacy influenced conceptual understanding via effort. Performance goal orientation negatively influenced conceptual understanding via attention and effort. Cognitive conflict influenced conceptual understanding directly as well as indirectly via situational interest.

• Journal of KIISE
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• v.42 no.11
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• pp.1339-1348
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• 2015

In a distributed system environment based on a service-oriented architecture, separate systems collaborate to achieve the goals of the entire system by using services provided other systems. A service quality violation from using one service can cause runtime system failure in the environment. The existing self-adaptation methods follow fault tolerance mechanism that responds to a failure after a service quality violation. In other words, these methods are limited to responsive action. Therefore, a service-dependability-case based self-adaptation mechanism is necessary to preserve the dependability of the self-adaptive system. This paper demonstrates that the service-dependability-case based self-adaptation mechanism is better than QoS(quality of service)-based self-adaptation with fault tolerance to preserve the dependability of the self-adaptive system. Additionally, this paper suggests a method to present and analyze service dependability by using GSN(Goal Structuring Notation) which is the existing modeling method for the presentation of assurance cases, an action mechanism adapted using an analysis result of service-dependability-cases, a methods of leveraging the service-dependability-case based self-adaptation mechanism by following the service's life cycle, and the framework architecture including the major components and the interactions between the components in the control loop of the self-adaptation process.

• Information Systems Review
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• v.12 no.3
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• pp.1-17
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• 2010

IT Systems based on Global Single Instance (GSI) can manage a corporation's internal information, resources and assets effectively and raise business efficiency through consolidation of their business process and productivity. But, It has also dangerous factor that IT system fault failure can cause a state of paralysis of a business itself, followed by huge loss of money. Many of studies have been conducted about fault-tolerance based on using redundant component. The concept of fault tolerance is rather simple but, designing and adopting fault-tolerance system is not easy due to uncertainty of a type and frequency of faults. So, Operational fault management that working after developed IT system is important more and more along with technical fault management. This study proposes the fault management process that including a pre-estimation method using TRM (Technical Reference Model) check point and event rule engine. And also proposes a effect of fault-free process through built fault management system to representative company of Hi-tech industry. After adopting fault-free process, a number of failure decreased by 46%, a failure time decreased by 56% and the Opportunity loss costs decreased by 77%.

• Journal of the Korea Institute of Military Science and Technology
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• v.1 no.1
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• pp.82-91
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• 1998

This paper presents a neural networks based approach for the problem of sensor failure detection and accommodation for ship without physical redundancy in the sensors. The designed model consists of two neural networks. The first neural network is responsible for the failure detection and the second neural network is responsible for the failure identification and accommodation. On the yaw rate sensor of ship, simulation results indicates that the proposed method can be useful as failure detector and sensor estimator.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1181-1185
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• 1990

A failure evaluation diagram to evaluate fatigue fracture was developed. The relation between the fatigue limit and the threshold stress intensity factor for the short-cracked specimens of various materials including a piping carbon steel can be rationally predicted by the proposed method. It is shown that the coupled failure evaluation diagram for fatigue and ductile fracture is expecially useful for evaluation of the flaw tolerance as well as the margin of the safety of the pressure vessel and piping. Further, accumulation of fatigue data will be needed to construct an accurate fatigue failure evaluation diagram.