Jung-Sik Hong

Damage detection using the Lipschitz exponent estimated by the wavelet transform: applications to vibration modes of a beam

Damage detection by the wavelet transform of the fundamental vibration mode receives much attention recently. Many investigations report successful applications of the wavelet transform in damage detection, but most of them appear to lack theoretical justifications. The objective of this contribution is to show the effectiveness of the wavelet transform by means of its capability to estimate the Lipschitz exponent. It is also addressed that the magnitude of the Lipschitz exponent can be used as a useful indicator of the damage extent. As a specific example, damaged beams are investigated both numerically and experimentally. The continuous wavelet transform (CWT) by a Mexican hat wavelet having two vanishing moments is utilized for the estimation of the Lipschitz exponent. The analysis by the CWT also gives a guideline to choose appropriate discrete wavelet transforms.

Joint reliability importance of k-out-of-n systems

Abstract Joint Reliability Importance (JRI) is investigated to provide information on the type and the degree of interactions between two components by identifying the sign and the size of it. In specific, JRI is analyzed for k -out-of- n systems with (i) independently identically distributed (IID) components, (ii) non-identical and independent components and (iii) pair-wise dependent components. The closed form solution of JRI is derived for IID components. By using the solution, the variations of JRI are investigated with respect to the level of redundancy ( n / k ). In non-identical and independent case, the point of sign change of JRI is obtained. It is also shown that the sign of JRI can be determined by the relationships between the Schur-convexity (concavity) and the JRI. For dependent case, only the pair-wise dependence is considered. As a result, the error caused by assuming statistical independence between pair-wise dependent components is shown to be measured by their covariance and JRI.

Economic-statistical design of 2-of-2 and 2-of-3 runs rule scheme

In this paper, we investigate the economic-statistical design method for the 2-of-2 runs rule and the 2-of-3 runs rule. The Markov chain approach is used to obtain the average run length and the process cycle time. In addition, a simplified algorithm is presented to search the optimal setting of the design parameters. A numerical example and sensitivity analysis are also provided to compare the performances of the runs rules. The results show that the use of runs rule scheme can reduce operating cost comparing with the Shewhart control chart while maintaining a good statistical performance. Copyright

Computation of joint reliability importance of two gate events in a fault tree

Abstract Joint reliability importance (JRI) of two gate events (GEs) is investigated along with its properties in a fault tree (FT). Computation of JRI of two GEs involves complexity because statistical dependency between GEs exists as a result of replication of basic events (BEs). To avoid complexity in computing the JRI, the topological relationships of two GEs in a FT are identified and classified into three classes. The explicit formula for the JRI of the two GEs is derived. JRI for each class is shown to be computed by using a conventional FT algorithm. By illustrating min. cut set representation of the bridge network, it is also shown that the degree of relationship between two min. cut sets can be measured by the JRI of the corresponding two GEs.

A Dynamic Anchor-Area Scheme Using a Timer Value and a Movement List for PCS Networks

A dynamic anchor-area (DAA) scheme is proposed to reduce the location management cost for PCS networks. Based on an Intra-LA location update (LU) scheme, the proposed DAA scheme utilizes a given timer value and a movement list. The DAA scheme considers a wider variety of mobile terminals movement pattern than the previous intra-LA LU scheme. Simulations confirm that the proposed scheme offers a significant reduction in the location management cost.

Design of location areas with QoS considerations in a cellular network

In this paper, we present a location area (LA) planning model which explicitly has more QoS-conscious constraints than any other models. In order to specify an acceptable level of QoS, paging delay time (PDT) and paging blocking rate (PBR) are introduced. The paging process is described by the M/M/c/K queuing system and queuing analysis is carried out to obtain PDT and PBR. Also, in the proposed model, the time-varying call arrival rates are used to define the paging load on each cell, which helps to reflect the pattern of incoming calls more precisely and subsequently to improve the QoS level. To evaluate the proposed model, some examples are solved along with the average rate model and the peak rate model. The results show that the proposed model has the capability to maintain the acceptable level of QoS with the reasonable location management cost, compared to other models. Also, the sensitivity analysis is performed to see the effect of PDT and PBR in the formulation and it turns out that both PBR and PDT are important elements of the QoS measure and influential to the location management cost.