• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.475-484
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• 2000

In this paper, new additional nonconforming modes for the improvement of bending behavior in the distorted 8 node hexahedral element and their effective modification method are studied. The rotational degrees of freedom are introduced by using a functional in which the rotations are independent variables. In an element formulation, the same interpolations are used in displacement and rotation fields, but nonconforming modes we applied only in displacement fields. To verify the developed element various numerical tests are carried out and test results show good behavior.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.4
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• pp.37-52
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• 2012

In this study, a new 4-node general shell element with 6 DOFs per node is presented. Drilling rotational degrees of freedom are introduced by the variational principle with an independent rotation field. In formulation of the element, substitute transverse shear strain fields are used to avoid shear locking, while four nonconforming modes are applied in the in-plane displacement fields as a remedy for membrane locking. In addition, a direct modification method for nonconforming modes is employed in the numerical implementation of nonconforming modes to represent constant strain states. A 9-points integration rule is adopted for volume integration in the computation of the element stiffness matrix. With the combined use of these techniques, the developed shell element has no spurious zero energy modes, and can represent a constant strain state. Several numerical tests are carried out to evaluate the performance of the new element developed. The test results show that the behavior of the elements is satisfactory.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.2
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• pp.19-25
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• 1985

By the combined use of reduced integration and addition of nonconforming displacement modes, a highly effective new plate element has been established. The displacement field of this element was formed by adding nonconforming modes only to transverse displacement component of Ahmad-Irons' element and the element matrices are computed by the numerical integrations with modified orders. Comparing with other elements, the superiority of the both NC 8-4.1 and NC 8-5.1 elements over the elements previously studied has been observed. The solutions with these elements converge to the true solutions very rapidly as the mesh is refined. These elements are also shown to be applicable to the wide range of thick and very thin plate problems.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.292-295
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• 2009

본 논문에서는 평판구조물의 정적 및 동적해석에 사용할 목적으로 성능이 향상된 평판유한요소를 제시하였다. 이 요소는 비적합변위형과 선택적 감차적분방법 그리고 대체전단변형률장을 복합적으로 적용하여 각각의 장점들을 포함하는 향상된 거동을 보여주고 있다. 또한 비적합변위형의 적용으로 발생되는 조각시험의 실패 문제점을 해결하기 위하여 직접수정법을 평판유한요소의 개선에 사용하였다. 대표적인 검증문제에 대한 수치해석작업을 통하여 본 연구에서 개발한 요소는 가상적인 제로에너지모드 및 전단잠김현상의 발생과 같은 문제를 나타내지 않음을 알 수 있었다. 특히 찌그러진 형상으로 모형화 한 경우에 있어서도 전단잠김현상이 발생하지 않았다. 본 연구에서 수행한 동적반응해석 시험에 있어서도 이론해와 잘 일치하는 결과를 보여주었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2078-2086
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• 1996

This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.311-320
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• 2005

In this paper an enhanced quadratic finite element for static and dynamic analysis of plate structures is presented. The performance of a proposed plate element is improved by the coupled use of non conforming displacement modes, the selective integration scheme, and the assumed shear strain fields. An efficient direct modification method is also applied to this element to solve the problem such as failure of the patch test due to the adoption of non conforming modes. The proposed quadratic finite element does not show any spurious mechanism and does not produce shear locking phenomena even with distorted meshes. It is shown that the results obtained by this element converged to analytical solutions very rapidly tough numerical tests for standard benchmark problems. It is also noted that this element is applicable to transient dynamic analysis of Mindlin plates.

• Computational Structural Engineering
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• v.10 no.2
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• pp.179-188
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• 1997

A 4-node element for efficient finite element analysis of plate bending is presented in this paper. This element is formulated based on Mindlin plate theory to take account of shear deformation. To overcome the overestimation of shear stiffness in thin Mindlin plate element, especially in the lower order element, five nonconforming displacement modes are added to the original displacement fields. The proposed nonconforming element does not possess spurious zero-energy mode and does not show shear locking phenomena in very thin plate even for distorted mesh shapes. It was recognized from benchmark numerical tests that the displacement converges to the analytical solutions rapidly and the stress distributions are very smooth. The element also provides good results for the case of high aspect ratio.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.2
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• pp.486-494
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• 1995

This paper introduces two kinds of new four-node quadrilateral axisymmetric elements with independently-assumed strains. They are formulated by the modified Hellinger-Reissner principle so as to employ incompatible displacements and assumed strains. In one of the present elements, the strains from incompatible displacements are corrected to pass the constant strain patch test. The other contains incompatible functions that are obtained from the element boundary condition. The elements are evaluated on the several problems of bending and material incompressibility with regular and distorted meshes. The results show that the new element performs excellently in deformation and stress calculation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2871-2882
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• 1994

Two kinds of 4-node plane stress/strain finite elements are presented in this work. They are derived from the modified Hellinger-Reissner variational principle so as to employ the internal incompatible displacement and independent stress fields, or the incompatible displacement and strain fields. The introduced incompatible functions are selected to satisfy the constant strain condition. The elements are evaluated on several problems of bending and material incompressibility with regular and distorted elements. The results show that the new elements perform excellently in the calculation of deformation and stresses.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.319-326
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• 2006

A new enhanced 8-node hybrid/mixed plane stress elements based on assumed stress fields and modifed shape functions has been presented. The assumed stress fields are derived from the non-conforming displacement modes, which are less sensitive to geometric distortion. Explicit expression of shape functions is modifed so that it can represent any quadratic fields in Cartesian coordinates under the same condition as 9-node isoparametric element. The newly developed element has been designated as 'HQ8-$14{\beta}$'. The presented element is compared with existing elements to establish its accuracy and efficiency. Over a wide range of mesh distortions, the element presented here is found to be exceptionally accurate in predicting displacements.