• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.4
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• pp.983-999
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• 2014

The structural design of the ships includes two main issues which should be checked carefully, namely the extreme structural response (yielding & buckling) and the fatigue structural response. Even if the corresponding failure modes are fundamentally different, the overall methodologies for their evaluation have many common points. Both issues require application of two main steps: deterministic calculations of hydro-structure interactions for given operating conditions on one side and the statistical post-processing in order to take into account the lifetime operational profile, on the other side. In the case of ultra large ships such as the container ships and in addition to the classical quasi-static type of structural responses the hydroelastic structural response becomes important. This is due to several reasons among which the following are the most important: the increase of the flexibility due to their large dimensions (Lpp close to 400 m) which leads to the lower structural natural frequencies, very large operational speed (> 20 knots) and large bow flare (increased slamming loads). The correct modeling of the hydroelastic ship structural response, and its inclusion into the overall design procedure, is significantly more complex than the evaluation of the quasi static structural response. The present paper gives an overview of the different tools and methods which are used in nowadays practice.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.431-453
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• 2013

The principal purpose of this paper is to present a novel two phases rational scenario applied in constructing an offshore monopod platform; in which the two phases are the all-ground horizontal construction phase and the post-construction phase. Concerning the all-ground construction phase, a brief investigation of its different stages, i.e., pre-fabrication, fabrication, pre-assembling, positioning, assembling, and surface finishing is introduced. The important practical aspects of such construction phase are investigated without going into the nitty-gritty of the details involved therein. Concerning the post-construction phase, a clear investigation of its sequential stages, i.e., lifting, moving and up-righting is introduced. A finite element model (FEM) of the monopod platform is created to perform the structural analysis necessary to decide the suspension points/devices and the handling scenario during the various stages of the post-construction phase on a rational wise. Such structural analysis is performed within the framework of the three dimensional quasi-static modeling and analysis aiming at simulating the realistic handling condition, and hence introducing a reliable physical interpretation of the numerical results. For the whole effort to be demonstrated efficiently, the results obtained are analyzed, the conclusions are presented, and few related recommendations are suggested.

• Computational Structural Engineering
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• v.9 no.3
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• pp.97-105
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• 1996

An integrated environment for optimum design has been developed using Motif. The integrated environment is composed of the preprocessor, the postprocessor and the optimization part. The preprocessor is part of making a finite element model for optimum structural design and the postprocessor displays results of optimum design and the optimization part is the part which execute optimization. It is designed to reduce user's difficulties in structural optimum design. It used Graphic User Interface for the concurrent representation of various inputs and outputs through the dialog box, mouse and keyboard. Structural optimum design can be done easily through dialog box, menu, concurrent representation of modeling process and results of structural optimum design can be understood easily through stress contour, deformed model and graph of cost function.

• Computational Structural Engineering
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• v.8 no.3
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• pp.51-57
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• 1995

A simplified stress analysis of perforated plates was carried out using homogenization technique. Homogenization technique, which introduced miroscale expansion in the standard finite element method, reconstructed the plate with regularly placed holes into a set of macroscale and microscale models. The microscale model helped compute homogenized material constants of the unit cell, which were used to compute macroscale displacements in the macroscale model. Also it was possible to compute the stress field of the plate using the microscale model. It was found that reasonable equivalent material constants were computed and that the required degrees of freedom was drastically reduced when homogenization technique was employed in the stress analyses. The microscale modeling in the homogenization technique provided a useful concept of pre- and post-processing in the stress analysis of perforated plates.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.565-570
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• 2007

Fiber reinforced polymer(FRP) composite decks are new to bridge applications and hence not much literature exists on their structural mechanical behavior. As there are many differences between numerical displacements through static analysis of the primary model and experimental displacements through static load tests, system identification (SI)techniques such as Neural Networks (NN) and support vector machines (SVM) utilized in the optimization of the FE model. During the process of identification, displacements were used as input while stiffness as outputs. Through the comparison of numerical displacements after SI and experimental displacements, it can note that NN and SVM would be effective SI methods in modeling an FRP deck. Moreover, two methods such as response surface method and iteration were proposed to optimize the estimated stiffness. Finally, the results were compared through the mean square error (MSE) of the differences between numerical displacements and experimental displacements at 6 points.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.248-254
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• 2015

The strength and fatigue life of Satin and Twill-woven CF/epoxy composite(CFRP) have been investigated. Damage mechanism fatigue method has been used to assess fatigue damage accumulation. It is based on measured residual stiffness and residual strength of carbon-fiber reinforced plastic(CFRP) laminates under cyclic loading. Fatigue damage evolution in composite laminates and predict fatigue life of the laminates were simulated by finite element analysis(FEA) method. The stress analysis was carried out in MSC patran/Nastran. A modified Hashin's failure criterion di rmfjapplied to predict the failure of the experimental data of fatigue life but a Ye-delamination criterion was ignored because of 2D modeling. Almost linear stiffness and strength degradation were observed during most of the fatigue process. These stress distribution data were adopted in the simulation to simulate fatigue behavior and estimate life of the laminates. From the results, the predicted fatigue life is more conservatively estimated than the experimental results.

• Journal of Korea Foundry Society
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• v.30 no.5
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• pp.196-200
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• 2010

The structural stress and fatigue behavior of tensile specimen containing internal shrinkage defect were modeled. Real shrinkage defect in casting was scanned by industrial CT (computed tomography), and subsequently its shape was simplified by ellipsoidal primitives for the structural analysis (S.S.M., shape simplification method). The analysis results were compared with the results by real shrinkage shape without any simplification process. It was possible to consider real shrinkage of casting in stress analysis and the method to predict fatigue life of casting with defect was proposed.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1318-1327
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• 2008

Geotechnical sites in urban areas may have embedded structures such as utility lines and underground concrete structures, which cause difficulties in site investigation. This study is a preliminary research to establish knowledge base for developing an optimal technique for site investigation in urban areas. Surface-wave method and resistivity survey, which are frequently adopted for non-destructive site-investigation for geotechnical sites, were investigated to characterize effects of adjacent structures. In case of surface wave method, patterns of wave propagation were investigated for typical sets of multi-layered geotechnical profiles by numerical simulation based on forward modeling theory and field experiments for small-size model tests and real-scale tests in the field. In case of resistivity survey, 3-D finite element analyses and field tests were performed to investigate effects of adjacent concrete structures. These theoretical and experimental researches for surface-wave method and resistivity survey resulted in establishing physical criteria to cause interference of adjacent structures in site investigation at urban areas.

• Computational Structural Engineering
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• v.7 no.3
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• pp.143-152
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• 1994

Superelement technique for structural analysis of large scale objects such as airplanes or vessels is effective especially in the harsh hardware environments. In this paper, a crane vessel of OHI 5000 which is capable of lifting 5000 tons in tie-backs and capable of revolving with 3000 tons is investigated in the view point of structural safety using superelements through the substructure scheme. Also an effective substructure procedure, a unique load extraction method and finite element modeling technique are demonstrated. Comprehensive reinforcement blueprints are derived based on the analysis results. Successful application of substructure technique is achieved through the structural analysis of the crane vessel. The analysis technique developed in this paper can be a guideline for similar large scale structures' relevant safety identification.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.121-125
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• 2010

In this study, we have constructed this algorithm that theoretical method for prediction performance of the internal ballastic analysis. And we have confirmed reliability, compared the value calculated by realized program with the value computed by modeling program. A basic concept of algorithm expresses combustion phenomenon to move each factor(node) according to the time increment like as Finite element method. And we have confirmed this realized program has sufficient possibility to utilize in the internal ballastic analysis.