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EditorialStructural Dynamics and Stability of Composite Structures

Sung-Cheon Han,1 Ireneusz Kreja,2 Guillermo Rus,3 and Gilson R. Lomboy4

1Department of Civil & Railroad Engineering, Daewon University College, Jecheon, Republic of Korea2Faculty of Civil and Environmental Engineering, Gdansk University of Technology, 80-952 Gdansk, Poland3Department of Structural Mechanics, University of Granada, Granada, Spain4Civil, Construction & Environmental Engineering, Iowa State University, Ames, IA 50011, USA

Correspondence should be addressed to Sung-Cheon Han; [email protected]

Received 3 August 2016; Accepted 3 August 2016

Copyright © 2016 Sung-Cheon Han et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

In structural applications, past few decades have seen out-standing advances in the use of composite materials includ-ing Functionally Graded Materials (FGM). Most structures,whether they are used in civil, marine, or aerospace engineer-ing, are subjected to dynamic loads during their operation.Therefore, Dynamic and Stability Analysis is receiving muchattention in academia and industries. Recent advances inDynamic and Stability Analysis have led to the developmentof macro-, micro-, and nanolaminated composites and FGMplates.

In M.-S. Park et al.’s paper, the authors investigated thesafety evaluation of a hybrid substructure for offshore windturbine. Towers and rotor-nacelles are being enlarged torespond to the need for higher gross generation of the windturbines. However, the accompanying enlargement of thesubstructure supporting these larger offshore wind turbinesmakes it strongly influenced by the effect of wave forces. Inthe present study, the hybrid substructure is suggested toreduce the wave forces by composing a multicylinder havingdifferent radii near free surface and a gravity substructureat the bottom of the multicylinder. In addition, the reactionforces acting on the substructure due to the very large deadload of the offshore wind turbine require very firm foun-dations. This implies that the dynamic pile-soil interactionhas to be fully considered. Therefore, ENSOFT Group V7.0is used to calculate the stiffness matrices on the pile-soilinteraction conditions.These matrices are then used togetherwith the loads at TP (Transition Piece) obtained from GH-Bladed for the structural analysis of the hybrid substructurebyANSYSASAS.The structural strength anddeformation are

evaluated to derive an ultimate structural safety of the hybridsubstructure for various soil conditions and show that thefirst few natural frequencies of the substructure are heavilyinfluenced by the wind turbine.Themodal analysis is carriedout through GH-Bladed to examine the resonance betweenthe wind turbine and the hybrid substructure.

The relationship between imperfections and shear buck-ling resistance of web plates with sectional damage caused bycorrosion is studied. To examine the imperfection effect onthe shear buckling resistance of a web plate with sectionaldamage, a series of a nonlinear finite element (FE) analyseswere carried out for a web plate with sectional damage, whichwas assumed as local corrosion damage. For consideringimperfections of the web plate in the girder, initial out-of-plane deformation was introduced in the FE analysis model.Using the FE analysis results, the changes in the shear buck-ling resistance of the web plate with sectional damage werequantitatively examined and summarized according to theaspect ratio, boundary conditions, and height of the damagedsection of the web plate. The effects of web imperfectionson the shear buckling resistance were evaluated to be littlecompared to that of the web plate without sectional damage.The shear buckling resistances were shown to significantlychange in the high-aspect-ratio web plate. A simple evalua-tion equation for the shear buckling resistance of a web platewith sectional damage was modified for use in the practicalmaintenance of a web plate in corrosive environments.

The rapid advances in high tech industries and theincreased demand for high precision and reliability of theirproduction environments call for larger structures and higher

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2016, Article ID 7468181, 2 pageshttp://dx.doi.org/10.1155/2016/7468181

2 Advances in Materials Science and Engineering

vertical vibration performance for high technology facilities.Therefore, there is an urgent demand for structural designand vertical vibration evaluation technologies for high techfacility structures. For estimating the microvibration perfor-mance for a clean room unit module in high technologyfacilities, this study performs the scale modeling experimentand analytical validation. First, the 1/2 scale model (width7500mm, depth 7500mm, and height 7250mm) for a cleanroom unit module is manufactured based on a mass-basedsimilitude law which does not require additional mass. Thedynamic test using an impact hammer is conducted to obtainthe transfer function of 1/2 scale model.The transfer functionderived from the test is compared with the analytical resultsto calibrate the analytical model. It is found that, unlikestatic analyses, the stiffness of embedded reinforcement mustbe considered for estimating microvibration responses. Thesimilitude law used in this study is validated by comparingthe full-scale analytical model and 1/2 scale analytical modelfor a clean room unit module.

In the present work, the vibration and buckling analysisof Functionally Graded Material (FGM) structures, using amodified 8-node shell element that allows for the effects oftransverse shear deformation, was improved. The propertiesof FGM vary continuously through the thickness directionaccording to the volume fraction of constituents definedby sigmoid function. The finite element is improved bythe combined use of different sets of collocation points forinterpolation of the strain components and assumed naturalstrains.Themodified 8-ANS shell element has been employedto study the effect of power law index on dynamic analysis ofFGM plates with various boundary conditions and bucklinganalysis under combined compressive, tensile, and shearloads and interaction curves of FGMplates subjected to com-bined loading is carried out. To overcome shear and mem-brane locking problems, the assumednatural strainmethod isemployed. In order to validate and compare the finite elementnumerical solutions, the reference results of plates based onNavier’s method and the series solutions of sigmoid FGM (S-FGM) plates are compared. Results of the present study showgood agreement with the reference results. The solutions ofvibration and buckling analysis are numerically illustrated ina number of tables and figures to show the influence of powerlaw index, side-to-thickness ratio, aspect ratio, types of loads,and boundary conditions in FGM structures.

Based on the finite element softwareABAQUSand gradedelement method, we developed a dummy node fracture ele-ment, wrote the user subroutinesUMATandUEL, and solvedthe energy release rate component of Functionally GradedMaterial (FGM) plates with cracks. An interface elementtailored for the virtual crack closure technique (VCCT) wasapplied. Fixed cracks and moving cracks under dynamicloads were simulated. The results were compared to otherVCCT-based analyses. With the implementation of a crackspeed function within the element, it can be easily expandedto the cases of varying crack velocities, without convergencedifficulty for all cases. Neither singular element nor collapsedelement was required. Therefore, due to its simplicity, theVCCT interface element is a potential tool for engineers

to conduct dynamic fracture analysis in conjunction withcommercial finite element analysis codes.

These papers represent an exciting, insightful observationinto the state of the art as well as emerging future topics,in this important interdisciplinary field. We hope that thisspecial issue would attract a major attention of the peers.

Acknowledgments

We would like to express our appreciation to all the authors,reviewers, and the Editorial Board members for the greatsupport to make this special issue possible.

Sung-Cheon HanIreneusz KrejaGuillermo Rus

Gilson R. Lomboy

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