• Journal of the Korean Society for Precision Engineering
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• v.30 no.10
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• pp.1079-1086
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• 2013

Optimal mount position of a front pillar trim considering heat resistant characteristics can be determined by two methods. One is conventional approximate optimization method which uses the statistical design of experiments (DOE) and response surface method (RSM). Generally, approximated optimum results are obtained through the iterative process by a trial and error. The quality of results depends seriously on the factors and levels assigned by a designer. The other is a methodology derived from previous work by the authors, which is called sequential design of experiments (SDOE), to reduce a trial and error procedure and to find an appropriate condition for using artificial neural network (ANN) systematically. An appropriate condition is determined from the iterative process based on the analysis of means. With this new technique and ANN, it is possible to find an optimum design accurately and efficiently.

• Korean Journal of Remote Sensing
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• v.23 no.1
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• pp.33-42
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• 2007

In this paper, an iterative MAP approach using a Bayesian model based on the lognormal distribution for image intensity and a GRF for image texture is proposed for despeckling the SAR images that are corrupted by multiplicative speckle noise. When the image intensity is logarithmically transformed, the speckle noise is approximately Gaussian additive noise, and it tends to a normal probability much faster than the intensity distribution. MRFs have been used to model spatially correlated and signal-dependent phenomena for SAR speckled images. The MRF is incorporated into digital image analysis by viewing pixel types as slates of molecules in a lattice-like physical system defined on a GRF Because of the MRF-SRF equivalence, the assignment of an energy function to the physical system determines its Gibbs measure, which is used to model molecular interactions. The proposed Point-Jacobian Iterative MAP estimation method was first evaluated using simulation data generated by the Monte Carlo method. The methodology was then applied to data acquired by the ESA's ERS satellite on Nonsan area of Korean Peninsula. In the extensive experiments of this study, The proposed method demonstrated the capability to relax speckle noise and estimate noise-free intensity.

• Steel and Composite Structures
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• v.42 no.1
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• pp.59-74
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• 2022

This study introduces a general reliability-based, performance-based design framework to design frames regarding their uncertainties and user-defined design goals. The Iterative-R method extracted from the main framework can designate a proper R (i.e., response modification factor) satisfying the design goal regarding target reliability index and pre-defined probability of collapse. The proposed methodology is based on FEMA P-695 and can be used for all systems that FEMA P-695 applies. To exemplify the method, multiple three-dimensional, four-story steel special moment-resisting frames are considered. Closed-form relationships are fitted between frames' responses and the modeling parameters. Those fits are used to construct limit state functions to apply reliability analysis methods for design safety assessment and the selection of proper R. The frameworks' unique feature is to consider arbitrarily defined probability density functions of frames' modeling parameters with an insignificant analysis burden. This characteristic enables the alteration in those parameters' distributions to meet the design goal. Furthermore, with sensitivity analysis, the most impactful parameters are identifiable for possible improvements to meet the design goal. In the studied examples, it is revealed that a proper R for frames with different levels of uncertainties could be significantly different from suggested values in design codes, alarming the importance of considering the stochastic behavior of elements' nonlinear behavior.

• Coupled systems mechanics
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• v.1 no.4
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• pp.361-379
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• 2012

This paper presents a fully coupled three-dimensional solver for the analysis of interaction between pulsatile flow and large deformation structure. A partitioned time marching algorithm is employed for the solution of the time dependent coupled discretised problem, enabling the use of highly developed, robust and well-tested solvers for each field. Conservative transfer of information at the fluid-structure interface is combined with an effective multi-predict-correct iterative scheme to enable implicit coupling of the interacting fields at each time increment. The three-dimensional unsteady incompressible fluid is solved using a powerful implicit time stepping technique and an ALE formulation for moving boundaries with second-order time accurate is used. A full spectrum of total variational diminishing (TVD) schemes in unstructured grids is allowed implementation for the advection terms and finite element shape functions are used to evaluate the solution and its variation within mesh elements. A finite element dynamic analysis of the highly deformable structure is carried out with a numerical strategy combining the implicit Newmark time integration algorithm with a Newton-Raphson second-order optimisation method. The proposed model is used to predict the wave flow fields of a particular flow-induced vibrational phenomenon, and comparison of the numerical results with available experimental data validates the methodology and assesses its accuracy. Another test case about three-dimensional biomedical model with pulsatile inflow is presented to benchmark the algorithm and to demonstrate the potential applications of this method.

• Journal of Digital Convergence
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• v.15 no.11
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• pp.447-454
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• 2017

Human desires start from the factors that make up the basic living environment. The development model of the safety guidelines will start from a sense of departure from collective psychology and systemic environment, at the time of inducing threats to threats. The design and methodology of the safety guidelines should be drawn up repeatedly by the sequence of iterative models, and the design methodology should be designed in the chronological order of the public services through the methodology of service design methodology. Various and complex threats attempt to derive insights from the user's perspective and to derive insight into the development of the safety guidelines and the sophistication of the user experience, and to extract insights from the perspective of a user's perspective and supervision model. This derived insight can be implemented as a multi-dimensional service model derived from the same problem consciousness methodology.

• Tribology and Lubricants
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• v.36 no.2
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• pp.96-104
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• 2020

The electric vehicle industry is rapidly developing because of enforced environmental regulations, and several studies have been conducted on the multispeed transmission to improve the fuel efficiency of electric vehicles. Among these studies, research on the power density improvement of electric vehicle transmission is critical. Thus, the optimal design of the gear train is necessary to enhance transmission efficiency. In this study, an optimal design methodology for the lightweight two-speed transmission of electric vehicles is proposed. Because a multispeed transmission has many operating conditions and equality and inequality constraints, a new gear design method that combines analytical and iterative methods is applied without using complex optimization algorithms. Sets of possible design variables are generated considering the operating conditions and various design variables. The modules and face width ratios of each stage gear that satisfy the corresponding operating conditions are analytically calculated. The volume of the gear train is calculated, evaluated, and arranged using these values to determine the optimal solution for minimizing the volume, and the proposed methodology is applied to the actual model to verify its effectiveness. The design of a two-speed transmission with multiple operating conditions and constraints without complicated optimization algorithms can be optimized.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.1
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• pp.18-27
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• 2019

The Advanced Power Reactor 1400 (APR1400) Steam Generator (SG) uses alloy 690 as a tube material and SA-508 Grade 3 Class 1 as a tubesheet material to form tube-to-tubesheet joint through hydraulic expansion process. In this paper, the residual stresses in the SG tube-to-tubesheet contact area was investigated by applying Model-Based System Engineering (MBSE) methodology and the V-model. The use of MBSE transform system description into diagrams which clearly describe the logical interaction between functions hence minimizes the risk of ambiguity. A theoretical and Finite Element Methodology (FEM) was used to assess and compare the residual stresses in the tube-to-tubesheet contact area. Additionally, the axial strength of the tube to tubesheet joint based on the pull-out force against the contact joint force was evaluated and recommended optimum autofrettage pressure to minimize residual stresses in the transition zone given. A single U-tube hole and tubesheet with ligament thickness was taken as a single cylinder and plane strain condition was assumed. An iterative method was used in FEM simulation to find the limit autofrettage pressure at which pull-out force and contact force are of the same magnitude. The joint contact force was estimated to be 20 times more than the pull-out force and the limit autofrettage pressure was estimated to be 141.85MPa.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1626-1637
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• 2020

This work covers an important point of the benchmark released by the expert group on Uncertainty Analysis in Modeling of Light Water Reactors. This ambitious benchmark aims to determine the uncertainty in light water reactors systems and processes in all stages of calculation, with emphasis on multi-physics (coupled) and multi-scale simulations. The Gesellschaft für Anlagen und Reaktorsicherheit methodology is used to propagate the thermal-hydraulic uncertainty of macroscopic parameters through TRACE5.0p3/PARCSv3.0 coupled code. The main innovative points achieved in this work are i) a new thermal-hydraulic model is developed with a highly-accurate 3D core discretization plus an iterative process is presented to adjust the 3D bypass flow, ii) a control rod insertion occurrence -which data is obtained from a real PWR test- is used as a transient simulation, iii) two approaches are used for the propagation process: maximum response where the uncertainty and sensitivity analysis is performed for the maximum absolute response and index dependent where the uncertainty and sensitivity analysis is performed at each time step, and iv) RESTING MATLAB code is developed to automate the model generation process and, then, propagate the thermal-hydraulic uncertainty. The input uncertainty information is found in related literature or, if not found, defined based on expert judgment. This paper, first, presents the Gesellschaft für Anlagen und Reaktorsicherheit methodology to propagate the uncertainty in thermal-hydraulic macroscopic parameters and, then, shows the results when the methodology is applied to a PWR reactor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.287-294
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• 2007

A static aeroelastic analysis for supersonic aircraft wing equipped with external store under the wing lower surface is performed using computational fluid dynamics (CFD) and computational structural technology(CST) coupling methodology. Two mapping algorithms, which are the pressure mapping algorithm and the displacement mapping algorithm, are used for CFD/CST coupling. A three-dimensional unstructured Euler code and finite element analysis program are used to calculate the flow properties and the structural displacements, respectively. The coupling procedure is repeated in an iterative manner until a specified convergence criterion is satisfied. Static aeroelastic analysis for a typical supersonic flight wing is performed and final converged wing configuration is obtained after several iterations.

• Journal of Information Technology Services
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• v.12 no.4
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• pp.219-234
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• 2013

We introduced a framework of information systems audit methodology and applied to IS projects based on RFID/USN in six public organizations in South Korea. An analysis of five IS implementation projects shows the iterative technical specific risks are disclosed. The key 14 risk factors categorized into 4 classifications (Project Management, application, database, system architecture) which are based on the established IT audit framework in order to extend to the technology (RFID/USN) specific framework and apply to the other case as well. The implications of these findings for audit research and practice are discussed.