• Steel and Composite Structures
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• 제42권1호
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• pp.75-90
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• 2022

The pointwise equilibrium polynomial (PEP) element considering local second-order effect has been widely used in direct analysis of many practical engineering structures. However, it was derived according to Euler-Bernoulli beam theory and therefore it cannot consider shear deformation, which may lead to inaccurate prediction for deep beams. In this paper, a novel beam-column element based on Timoshenko beam theory is proposed to overcome the drawback of PEP element. A fifth-order polynomial is adopted for the lateral deflection of the proposed element, while a quadric shear strain field based on equilibrium equation is assumed for transverse shear deformation. Further, an additional quadric function is adopted in this new element to account for member initial geometrical imperfection. In conjunction with a reliable and effective three-dimensional (3D) co-rotational technique, the proposed element can consider both member initial imperfection and transverse shear deformation for second-order direct analysis of frame structures. Some benchmark problems are provided to demonstrate the accuracy and high performance of the proposed element. The significant adverse influence on structural behaviors due to shear deformation and initial imperfection is also discussed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.367-375
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• 2020

This paper presents an integrated analysis about dynamic performance of a Floating Offshore Wind Turbine (FOWT) OC4 DeepCwind with semi-submersible platform under real sea environment. The emphasis of this paper is to investigate how the wave mean drift force and slow-drift wave excitation load (Quadratic transfer function, namely QTF) influence the platform motions, mooring line tension and tower base bending moments. Second order potential theory is being used for computing linear and nonlinear wave effects, including first order wave force, mean drift force and slow-drift excitation loads. Morison model is utilized to account the viscous effect from fluid. This approach considers floating wind turbine as an integrated coupled system. Two time-domain solvers, SIMA (SIMO/RIFLEX/AERODYN) and FAST are being chosen to analyze the global response of the integrated coupled system under small, moderate and severe sea condition. Results show that second order mean drift force and slow-drift force will drift the floater away along wave propagation direction. At the same time, slow-drift force has larger effect than mean drift force. Also tension of the mooring line at fairlead and tower base loads are increased accordingly in all sea conditions under investigation.

• 한국항만경제학회지
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• 제17권1호
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• pp.27-51
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• 2001

The purpose of this paper is to investigate the productive efficiency of world container ports by using the DEA (Data Envelopment Analysis) method and raw data from previous research in measuring the international competitiveness of world container ports. Ports have to cope with rapid changes in shipping environments. In order for a port to compete in the global market, it must provide port services promptly and accurately. Basically, there are two approaches to measuring the international competitiveness of a container port. First, there is the traditional productivity analysis method, which analyzes productivity based on the container port's facilities (efficiency, selectivity, land availability), and by its general capacity (handling ability, storage capacity, terminal productivity). Second there is multi-attribute utility analysis, which considers several elements including the reasons for selecting particular container ports and factors determining international competitiveness. This paper follows the first method (traditional productivity analysis) and extends the limitation of previous studies by using the DEA method newly, and suggesting: the relative productive efficiency of container ports. The main results of this paper are as follows: First, the results of the DEA analysis in terms of world container ports matches that of a previous study (Jun et al., 1993) at a level of 35%. The low ratio is due to the constrained set of input-output elements, the result of only twenty container ports being analyzed in this paper. Second, the result of the DEA analysis in terms of North-East Asia's container ports matches with that of a previous study (Ha, 1996) at a level of 100 percent. Therefore we can conclude that the DEA analysis is the best measurement method for international competitiveness. Policy implications for this study are as follows: First, when port authorities want to measure the international competition power of container ports and enhance their productive efficiency, they should consider the traditional method and newly introduce the DEA method. Second, according to the analysis results of the DEA method, pen authorities should recommend benchmarking ports as reference ports in order to enhance the productive efficiency of container ports that show an efficiency score of below 1.

• 한국자동차공학회논문집
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• 제7권5호
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• pp.268-277
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• 1999

Impulsive acoustic and vibration signals within gear are often induced by impacting of fault tooths in gear. Thus the detection of these impulses can be useful for fault diagnosis. Recently there is an increasing trend towards the use of higher order statistics for fault detection within mechanical systems based on the observation that impulsive signals then to increase the kurtosis values. We show that the fourth order Wigner Moment Spectrum, called the Wigner Trispectrum, has found superior detection performance to second order Wigner distribution for typical impulsive signals in a condition monitoring application. These methods are also applied to data sets measured within an industrial gear box.

• Structural Engineering and Mechanics
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• 제42권2호
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• pp.175-189
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• 2012

This paper presents an algorithm for structural reliability with the response surface method. For this aim, an approach with three stages is proposed named as improved response surface method. In the algorithm, firstly, a quadratic approximate function is formed and design point is determined with First Order Reliability Method. Secondly, a point close to the exact limit state function is searched using the design point. Lastly, vector projected method is used to generate the sample points and Second Order Reliability Method is performed to obtain reliability index and probability of failure. Five numerical examples are selected to illustrate the proposed algorithm. The limit state functions of three examples (cantilever beam, highly nonlinear limit state function and dynamic response of an oscillator) are defined explicitly and the others (frame and truss structures) are defined implicitly. ANSYS finite element program is utilized to obtain the response of the structures which are needed in the reliability analysis of implicit limit state functions. The results (reliability index, probability of failure and limit state function evaluations) obtained from the improved response surface are compared with those of Monte Carlo Simulation, First Order Reliability Method, Second Order Reliability Method and Classical Response Surface Method. According to the results, proposed algorithm gives better results for both reliability index and limit state function evaluations.

• 정보기술응용연구
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• 제1권
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• pp.173-211
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• 1999

The task of classification permeates all walks of life, from business and economics to science and public policy. In this context, nonlinear techniques from artificial intelligence have often proven to be more effective than the methods of classical statistics. The objective of knowledge discovery and data mining is to support decision making through the effective use of information. The automated approach to knowledge discovery is especially useful when dealing with large data sets or complex relationships. For many applications, automated software may find subtle patterns which escape the notice of manual analysis, or whose complexity exceeds the cognitive capabilities of humans. This paper explores the utility of a collaborative learning approach involving integrated models in the preprocessing and postprocessing stages. For instance, a genetic algorithm effects feature-weight optimization in a preprocessing module. Moreover, an inductive tree, artificial neural network (ANN), and k-nearest neighbor (kNN) techniques serve as postprocessing modules. More specifically, the postprocessors act as second0order classifiers which determine the best first-order classifier on a case-by-case basis. In addition to the second-order models, a voting scheme is investigated as a simple, but efficient, postprocessing model. The first-order models consist of statistical and machine learning models such as logistic regression (logit), multivariate discriminant analysis (MDA), ANN, and kNN. The genetic algorithm, inductive decision tree, and voting scheme act as kernel modules for collaborative learning. These ideas are explored against the background of a practical application relating to financial fraud management which exemplifies a binary classification problem.

• Steel and Composite Structures
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• 제4권6호
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• pp.419-435
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• 2004

The safety level of a structural system designed per code specifications can not be inferred directly from the reliability of members due to the load redistribution and nonlinear inelastic structural behavior. Comparison of the system and member reliability, which is scarce in the literature, is likely to indicate any possible inconsistency of design codes in providing safe and economical designs. Such a comparative study is presented in this study for moment resisting two-dimensional steel frames designed per AISC LRFD Specifications. The member reliability is evaluated using the resistance of the beam-column element and the elastic load effects that indirectly accounts for the second-order effects. The system reliability analysis is evaluated based on the collapse load factor obtained from a second-order inelastic analysis. Comparison of the system and member reliability is presented for several steel frames. Results suggest that the failure probability of the system is about one order of magnitude lower than that of the most critically loaded structural member, and that the difference between the system and member reliability depends on the structural configuration, degree of redundancy, and dead to live load ratio. Results also suggest that the system reliability is less sensitive to initial imperfections of the structure than the member reliability. Therefore, the system aspect should be incorporated in future design codes in order to achieve more reliability consistent designs.

• Journal of Mechanical Science and Technology
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• 제16권7호
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• pp.959-965
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• 2002

Effective hydraulic conductivity of a statistically anisotropic heterogeneous medium is obtained for steady two-dimensional flows employing stochastic analysis. Flow equations are solved up to second order and the effective conductivity is obtained in a semi-analytic form depending only on the spatial correlation function and the anisotropy ratio of the hydraulic conductivity field, hence becoming a true intrinsic property independent of the flow field. Results are obtained using a statistically anisotropic Gaussian correlation function where the anisotropy is defined as the ratio of integral scales normal and parallel to the mean flow direction. Second order results indicate that the effective conductivity of an anisotropic medium is greater than that of an isotropic one when the anisotropy ratio is less than one and vice versa. It is also found that the effective conductivity has upper and lower bounds of the arithmetic and the harmonic mean conductivities.

• 한국해양공학회지
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• 제20권5호
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• pp.30-35
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• 2006

In tire presence of incident waves with different frequencies, there are second order sum and difference frequency wave exciting forces due to the nonlinearity of tire incident waves. Although the magnitude of these nonlinear wave forces are small, they act on TLPs at sum and difference frequencies away from those of the incident waves. So, the second order sum and difference frequency waveexciting forces occurring close to tire natural frequencies of TLPs often give greater contributions to high and law frequency resonant responses. Nonlinear motion responses and tension variations in the time domain are analyzed by solving the motion equations with nonlinear wave exciting forces using tire numerical analysismethod. The numerical results of time domain analysis for the nonlinear wave exciting forces on the ISSC TLP in regular waves are compared with the numerical and experimental ones of frequency domain analysis. The results of this comparison confirmed tire validity of the proposed approach.

• Steel and Composite Structures
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• 제24권3호
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• pp.339-349
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• 2017

In this paper, a conventional refined plastic hinge analysis is improved to account for the effects of local buckling and lateral-torsional buckling. The degradation of flexural strength caused by these effects is implicitly considered using practical LRFD equation. The second-order effect is captured using stability functions to minimize modeling and solution time. An incremental-iterative scheme based on the generalized displacement control method is employed to solve the nonlinear equilibrium equations. A computer program is developed to predict the second-order inelastic behavior of space steel frames. To verify the accuracy and efficiency of the proposed program, the obtained results are compared with the existing results and those generated using the commercial finite element package ABAQUS. It can be concluded that the proposed program proves to be a reliable and effective tool for daily use in engineering design.