• Structural Engineering and Mechanics
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• v.41 no.2
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• pp.157-181
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• 2012

The paper presents a review of the application of the newly proposed mixed finite element model for seismic simulation of different types of composite frame structures. To evaluate the performance of the element, a comparison with displacement-based and force-based models is conducted. The study revealed that the mixed model is superior to the others in terms of both speed of convergence and numerical stability, and is therefore considered the most practical approach for modeling of composite structures. In this model, the element is derived using independent force and displacement shape functions. The nonlinear response of the frame element is based on the section discretization into fibers with uniaxial material models. The interfacial behavior is modeled using an inelastic interface element. Numerical examples to clarify the advantages of the model are presented for the following structural applications: anchored reinforcing bar problems, composite steel-concrete girders with deformable shear connectors, beam on elastic foundation elements, R/C girders strengthened with FRP sheets, R/C beam-columns with bond-slip, and prestressed concrete girders. These studies confirmed that the model represents a major advancement over existing elements in simulating the inelastic behavior of composite structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.1 s.244
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• pp.18-25
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• 2006

The purpose of this research work is to demonstrate a successful application of hybrid-mixed formulation and nodeless degrees of freedom in developing a very accurate in-plane curved beam element for free vibration analysis. To resolve the numerical difficulties due to the spurious constraints, the present element, based on the Hellinger-Reissner variational principle and considering the effect of shear deformation, employed consistent stress parameters corresponding to cubic displacement polynomials with additional nodeless degrees. The stress parameters were eliminated by the stationary condition, and the nodeless degrees were condensed by Guyan Reduction. Several numerical examples indicated that the property of the mass matrix as well as that of the stiffness matrix have a great effect on the numerical performance. The element with consistent mass matrix produced best results on convergence and accuracy in the numerical analysis of Eigenvalue problems. Also, the higher-order mixed curved beam element showed a superior numerical behavior for the free vibration analyses.

• Applied Chemistry for Engineering
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• v.34 no.5
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• pp.501-506
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• 2023

Oleogel and oleogel emulsions of sunflower oil were prepared using sucrose ester and ceramide as mixed gelators. The crystal structure of the gelator in the oleogels and oleogel emulsion formulations was observed with a polarized optical microscope, and the dispersion form of water was confirmed with confocal laser scanning microscopy. Through the DSC thermogram analysis, it was confirmed that the crystal structure of ceramide disappeared when sucrose ester and ceramide were mixed, and the crystallinity of the mixed gelator increased further when water was added to the formulation. Changes in rheological properties such as viscosity and viscoelasticity according to the ratio of sucrose ester, ceramide, and water in the formulation were examined. As the content of ceramide and water increased, the viscosity, storage modulus, and loss modulus all increased, and the stability of the formulation also tended to increase.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.888-895
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• 2000

As conventional grouting materials for the sheath such as cement slurry or cement-mortar are mixed and pumped in site, those harden with bleeding or shrinkage and meets low compressive strength. Also the materials haven't always same cements, sand size distributions, additives in site, so those materials have unstable quality properties. We have studies on ready-mixed-mortar for grouting pretensioned or post-tensioned cables and rods to encapsulate the steel so that we have developed a formulation of specially selected, flowable, shrinkage-compensating materials.

• Composites Research
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• v.36 no.2
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• pp.117-125
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• 2023

This paper proposes a new finite element formulation based on enhanced first-order shear deformation theory including the transverse normal strain effect via the mixed formulation (EFSDTM-TN) for the effective thermo-mechanical analysis of laminated composite structures. The main objective of the EFSDTM-TN is to provide an accurate and efficient solution in describing the thermo-mechanical behavior of laminated composite structures by systematically establishing the relationship between two independent fields (displacement and transverse stress fields) via the mixed formulation. Another key feature is to consider the thermal strain effect without additional unknown variables by introducing a refined transverse displacement field. In the finite element formulation, an eight-node isoparametric plate element is newly developed to implement the advantage of the EFSDTM-TN. Numerical solutions for the thermo-mechanical behavior of laminated composite structures are compared with those available in the open literature to demonstrate the numerical performance of the proposed finite element model.

• Computational Structural Engineering
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• v.1 no.1
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• pp.67-78
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• 1988

A new method of element decomposition is suggested for simple, efficient, and generalized formulation of shell finite elements. The kernel of the method is to decompose conceptually the actual element into a translational element and a difference element. The actual element is obtained by combining the two component elements. The derived element can be classified into three basic types depending on how the element is decomposed. A few complementary measures, to remove locking phenomena and thus improve the performance of the elements, have been studied. They are reduced integration, addition of internal degrees of freedom, and mixed formulation. A rational method of controlling spurious zero energy modes has also been devised. Validity and efficiency of the element with or without complementary measures have been examined through a series of numerical studies.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.147-161
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• 2023

Based on the ideas of variational differential quadrature (VDQ) and finite element method (FEM), a numerical approach named as VDQFEM is applied herein to study the large deformations of plate-type structures under static loading with arbitrary shape hole made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) in the context of higher-order shear deformation theory (HSDT). The material properties of composite are approximated based upon the modified Halpin-Tsai model and rule of mixture. Furthermore, various FG distribution patterns are considered along the thickness direction of plate for GPLs. Using novel vector/matrix relations, the governing equations are derived through a variational approach. The matricized formulation can be efficiently employed in the coding process of numerical methods. In VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element. As the last step, the assemblage procedure is performed to derive the set of governing equations which is solved via the pseudo arc-length continuation algorithm. Also, since HSDT is used herein, the mixed formulation approach is proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Rectangular and circular plates under various boundary conditions with circular/rectangular/elliptical cutout are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the nonlinear maximum deflection-transverse load amplitude curve are studied.

• Korean Journal of Environmental Agriculture
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• v.15 no.1
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• pp.105-115
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• 1996

In this paper, we reviewed the degradation factors of diazinon which was known to be easily degraded by soil microorganisms and lost of its activity. Under submerged soil condition, the contribution of microorganisms to diazinon degradation was about 40% and these microorganisms preferred soil humus as substrates to diazinon itself. The effect of monooxygenase activity in submerged soil was more important than esterase activity on diazinon degradation and these enzymes were inhibited by several chemicals such as piperonyl butoxide(PBO), EPN and tricyclazole. From these results, new formulation type of diazinon (PBO and triphenyl phosphate were added to commercial diazinon formulation by 0.1% respectively.) and diazinon mixture formulation (diazinon was mixed with EPN, tricyclazole and carbofuran in equal amount) were prepared. The new formulation type of diazinon showed better insecticidal activity by 12% and more delayed diazinon degradation in ten days than commercial diazinon.

• Honam Mathematical Journal
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• v.42 no.1
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• pp.17-35
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• 2020

In this paper we introduce and consider a new class of variational inequalities with four operators. This class is called the extended general mixed quasi variational inequality. We show that the extended general mixed quasi variational inequality is equivalent to the fixed point problem. We use this alternative equivalent formulation to discuss the existence of a solution of extended general mixed quasi variational inequality and also develop several iterative methods for solving extended general mixed quasi variational inequality and its variant forms. We consider the convergence analysis of the proposed iterative methods under appropriate conditions. We also introduce a new class of resolvent equation, which is called the extended general implicit resolvent equation and establish an equivalent relation between the extended general implicit resolvent equation and the extended general mixed quasi variational inequality. Some special cases are also discussed.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.567-577
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• 2005

Several methods for improving the interlaminar strength and fracture toughness of composite materials are developed. Through-the-thickness stitching is considered one of the most common ways to prevent delamination. Stitching significantly increases the Mode I fracture toughness and moderately improves the Mode II fracture toughness. An analytical model has been developed for simulating the behavior of stitched double cantilever beam specimen under various loading conditions. For z-directional load and moment about the y-axis the numerical solutions are compared with the exact solutions. The derived formulation shows good accuracy when the relative error of displacement and rotation between numerical and exact solution were calculated. Thus we can use the present model with confidence in analyzing other problems involving stitched beams.