• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.611-617
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• 2010

A complex system involves a large number of design variables, and its operation is non-linear. To explore the characteristics in its design space, a Kriging meta-model can be utilized; this model has replaced expensive computational analysis that was performed in traditional parametric design optimization. In this study, a Kriging meta-model with a computational orthogonal array for the design of experiments was developed to optimize the fatigue life of a turbine blade whose behavior under cyclic rotational loads is significantly non-linear. The results not only show that the maximum fatigue life is improved but also indicate that the accuracy of computational analysis is achieved. In addition, the robustness of the results obtained by six-sigma optimization can be verified by comparison with the results obtained by performing Monte Carlo simulations.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.49-57
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• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• Journal of radiological science and technology
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• v.38 no.3
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• pp.237-244
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• 2015

Health professionals in nuclear medicine were known that they get high radiation exposure. To reduce radiation exposure, using shielding materials is needed. In this study, we analyzed the shielding effect about apron during 18F-FDG treatment by using simulation based on Monte Carlo techniques and actual measurement. As a result, absorbed dose distribution of organ varies with handling position of the source. Dose reduction ratio by lead thickness of apron tended to decease, when handling position of the source come close to organ and away from radiation source for simulation. In the case of actual measurement with the dosimetry device, It showed that mean spatial dose distribution was different due to characteristics of dosimetry device. However, spatial dose rate was exponentially reduced according to distance with increasing lead content.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.6
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• pp.108-116
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• 2008

In this paper, we propose an algorithm that can estimate the distance using disparity based on stereo vision system, even though the obstacle is located in long ranges as well as short ranges. We use sub-pixel interpolation to minimize quantization errors which deteriorate the distance accuracy when calculating the distance with integer disparity, and also we use enhanced adaptive fuzzy strong tracking Kalman filter(EAFSTKF) to improve the distance accuracy and track the path optimally. The proposed method can solve the divergence problem caused by nonlinear dynamics such as various vehicle movements in the conventional Kalman filter(CKF), and also enhance the distance accuracy and reliability. Our simulation results show that the performance of our method improves by about 13.5% compared to other methods in point of root mean square error rate(RMSER).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.4
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• pp.355-362
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• 2008

A reliability model of Level II AFDA is proposed to analyze the wave run-up occurring by the interaction of incident waves and sloped coastal structures. The reliability model may be satisfactorily calibrated by Level III Monte-Carlo simulation. Additionally, the partial safety factors of random variables related to wave run-up can be straightforwardly evaluated by the inverse-reliability method that use influence coefficients and uncertainties of random variables, and target probability of failure. In particular, a design equation for wave run-up is derived in the same form as that of deterministic design method so that the reliability-based design method of Level I may be applied easily. Finally, it is confirmed that results redesigned by the reliability-based design method of Level I with partial safety factors suggested in this paper are satisfactorily compared with results of CEM(2006) as well as those of Level II AFDA.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.52-62
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• 2013

A stochastic Markov process (MP) model has been developed for evaluating the probability of failure of the armor unit of rubble-mound breakwaters as a function of time. The mathematical MP model could have been formulated by combining the counting process or renewal process (CP/RP) on the load occurrences with the damage process (DP) on the cumulative damage events, and applied to the armor units of rubble-mound breakwaters. Transition probabilities have been estimated by Monte-Carlo simulation (MCS) technique with the definition of damage level of armor units, and very well satisfies some conditions constrained in the probabilistic and physical views. The probabilities of failure have been also compared and investigated in process of time which have been calculated according to the variations of return period and safety factor being the important variables related to design of armor units of rubble-mound breakwater. In particular, it can be quantitatively found how the prior damage levels can effect on the sequent probabilities of failure. Finally, two types of methodology have been in this study proposed to evaluate straightforwardly the repair times which are indispensable to the maintenance of armor units of rubble-mound breakwaters and shown several simulation results including the cost analyses.

• Tunnel and Underground Space
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• v.22 no.3
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• pp.214-220
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• 2012

Deformation behaviour of rock mass around an opening measured during tunnel excavation is very important in order to assess the stability of the tunnel. Unfortunately displacement measured only after the installation of displacement measuring device can be acquired, which results in inevitably excluding the pre-displacement occurred and accumulated before the displacement measuring devices are installed. So it is very important to consider the pre-displacement based on the elapsed time before zero reading after deformation behaviour started. In this study, the accuracy of total estimated displacement depending on the distance between face and measurement position is calculated by statistical non-linear fitting on measurable displacement data. Besides, the influence of the unavoidable measurement error is considered by using Monte-Carlo simulation. As a result, the faster the initial reading started and the smaller the measurement error is, the higher the accuracy of estimating total displacement is obtained.

• Communications for Statistical Applications and Methods
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• v.17 no.4
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• pp.541-550
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• 2010

The $L_1$-regression estimator is susceptible to the leverage points, even though it is highly robust to the vertical outliers. This article is concerned with the improvement of robustness of the $L_1$-estimator. To improve its robustness, in terms of the breakdown point, we attempt to dampen the influence of the leverage points by means of reducing the weights corresponding to the leverage points. In addition the algorithm employs the linear scaling transformation technique, for higher computational efficiency with the large data sets, to solve the linear programming problem of $L_1$-estimation. Monte Carlo simulation results indicate that the proposed algorithm yields $L_1$-estimates which are robust to the leverage points as well as the vertical outliers.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.229-236
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• 2016

For this research, the trajectory of a projectile was simulated via the multibody dynamics analysis of a self-propelled mortar. The dynamic model was composed of a mortar model and a vehicle model, and was simulated using the RecurDyn program. Interior ballistic was applied to the mortar model, and exterior ballistic was conducted by Matlab using the simulation results of the interior trajectory. Through repetitive Monte-Carlo simulations, the accuracy of the mortar was analyzed by considering variations in the aiming angle and vehicle dynamic response.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.26-37
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• 2004

Consistent and realistic error covariance information is important for position estimation, error analysis, fault detection, and integer ambiguity resolution for differential GNSS. In designing a position domain carrier-smoothed-code filter where incremental carrier phases are used for time-propagation, formulation of consistent error covariance information is not easy due to being bounded and temporal correlation of propagation noises. To provide consistent and correct error covariance information, this paper proposes two recursive filter algorithms based on carrier-smoothed-code techniques: (a) the stepwise optimal position projection filter and (b) the stepwise unbiased position projection filter. A Monte-Carlo simulation result shows that the proposed filter algorithms actually generate consistent error covariance information and the neglection of carrier phase noise induces optimistic error covariance information. It is also shown that the stepwise unbiased position projection filter is attractive since its performance is good and its computational burden is moderate.