• Structural Engineering and Mechanics
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• v.8 no.2
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• pp.207-231
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• 1999

A versatile 4-node shell element which is useful for the analysis of arbitrary shell structures is presented. The element is developed by flat shell approach, i.e., by combining a membrane element with a Mindlin plate element. The proposed element has six degrees of freedom per node and permits an easy connection to other types of finite elements. In the plate bending part, an improved Mindlin plate has been established by the combined use of the addition of non-conforming displacement modes (N) and the substitute shear strain fields (S). In the membrane part, the nonconforming displacement modes are also added to the displacement fields to improve the behavior of membrane element with drilling degrees of freedom and the modified numerical integration (M) is used to overcome the membrane locking problem. Thus the element is designated as NMS-4F. The rigid link correction technique is adopted to consider the effect of out-of-plane warping. The shell element proposed herein passes the patch tests, does not show any spurious mechanism and does not produce shear and membrane locking phenomena. It is shown that the element produces reliable solutions even for the distorted meshes through the analysis of benchmark problems.

• Land and Housing Review
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• v.4 no.3
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• pp.271-277
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• 2013

The BNWF (Beam on Nonlinear Winkler Foundation) model is one of the simplest idealizations for a pile embedded in soil as it ignores the continuity of the soil. This method is difficult to model the behavior of pile group foundation subjected to lateral loading. The limitation can be overcome with the utilization of the finite element method (FEM) or finite different method (FDM) to represent a pile element embedded in a soil medium. Both the ground and piles are modeled with soild elements. The solid elements, which do not have rotational degree of freedom, is not appropriate for modeling piles. It can be overcome by substantially increasing the number of elements, which can be prohibitive for 3D modeling. This paper used the beam element and rigid link incorporated in the OpenSees to model the pile. The accuracy of the model is validated through comparison with lateral load test and BNWF analysis. It is shown that the method can capture the measured behavior accurately. It is therefore recommended to be used in group pile analyses.

• Journal of the Korean Society for Marine Environment & Energy
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• v.13 no.2
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• pp.83-90
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• 2010

The hydrodynamic interaction of two floating bodies in waves freely floating or connected by a rigid link is studied by using a boundary element method in the frequency-domain. The exact two-body hydrodynamic coefficients of added mass, wave damping and exciting force are calculated from the radiation-diffraction potential solution of the improved Green integral equation associated with the free surface Green function. The irregular frequencies in the conventional Green integral equation make it difficult to predict the physical resonance of the fluid in the gap between two bodies floating side by side. However, the improved Green integral equation employed in this study is free of irregular frequencies and always yields the exact solution of the multi-body radiation-diffraction potential boundary value problem. The 6 degree-of-freedom motions of two bodies freely floating side by side or connected parallel by a rigid link have been calculated for the incident wave frequencies ranging from 0.1 to 5 radians per second in head, left and right bow quartering seas. The 6-component load of the rigid link have also been presented.

• Steel and Composite Structures
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• v.51 no.3
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• pp.305-323
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• 2024

Previous experimental studies have effectively demonstrated the remarkable efficiency of the stiffened channel link in connecting circular columns and I-shaped beams. This research aims to present design criteria and assess the seismic properties of this specific connection type through numerical modeling. Various parameters, including stiffener type and geometric properties of the stiffened channel element, were duly taken into account. The findings from over 136 nonlinear finite element analyses (FEAs) reveal that the recommended detailing scheme reliably satisfies all the regulations specified for rigid beam-to-column connections in special moment frames.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.533-538
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• 1991

In the design and operation of robot arms with flexible links, the equations of motion are required to exactly model the interaction between rigid motion and elastic motion and to be formulated efficiently. Thus, the flexible link is represented on the basis of the D-H rigid link representation to measure the elastic deformation. The equations of motion of robot arms, which are configured by the generalized coordinates of elastic and rigid degrees of freedom, are formulated by using F.E.M. to model complex shaped links systematically and by eliminating elastic mode of higher order that does not largely affect motion to reduce the number of elastic degree of freedom. Finally, presented is the result of simulation to flexible robotic arm whose joints are controlled by direct or PD control,

• 제어로봇시스템학회:학술대회논문집
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• 1990.10a
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• pp.18-23
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• 1990

In this paper, the dynamic modeling and a tip-position controller of a single-link flexible manipulator are developed. To design the controller of a flexible manipulator, at first, it is required to obtain the accurate dynamic model of manipulator describing both rigid motion and flexible vibration. For this purpose, FEM(Finite Element Method) and Lagrange approach are utilized to obtain the dynamic model. After obtaining the dynamic model of a single-link manipulator, a controller which computes the input torque to perform the desired trajectory is developed using neural network.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1165-1166
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• 2013

• Steel and Composite Structures
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• v.34 no.5
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• pp.625-641
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• 2020

The realistic modeling of the beam-column semi-rigid connection in steel frames attracted the attention of many researchers in the past for the seismic analysis of semi-rigid frames. Comparatively less studies have been made to investigate the behavior of steel frames with semi-rigid connections under different types of earthquake. Herein, the seismic behavior of semi-rigid steel frames is investigated under both far and near-field earthquakes. The semi-rigid connection is modeled by the multilinear plastic link element consisting of rotational springs. The kinematic hysteresis model is used to define the dynamic behavior of the rotational spring, describing the nonlinearity of the semi-rigid connection as defined in SAP2000. The nonlinear time history analysis (NTHA) is performed to obtain response time histories of the frame under scaled earthquakes at three PGA levels denoting the low, medium and high-level earthquakes. The other important parameters varied are the stiffness and strength parameters of the connections, defining the degree of semi-rigidity. For studying the behavior of the semi-rigid frame, a large number of seismic demand parameters are considered. The benchmark for comparison is taken as those of the corresponding rigid frame. Two different frames, namely, a five-story frame and a ten-story frame are considered as the numerical examples. It is shown that semi-rigid frames prove to be effective and beneficial in resisting the seismic forces for near-field earthquakes (PGA ≈ 0.2g), especially in reducing the base shear to a considerable extent for the moderate level of earthquake. Further, the semi-rigid frame with a relatively weaker beam and less connection stiffness may withstand a moderately strong earthquake without having much damage in the beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.50-60
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• 2013

Dynamic response of steel plate girder bridges by KL-510 design truck in KHBDC considering the road surface roughness of bridges and bridge-vehicle interaction is investigated. Simply supported steel plate girder bridges with span length of 20m, 30m, and 40m from "Standard Highway Bridge Superstructure" published by the Korean Ministry of Construction are used for a bridge model, and ten sets of the road surface roughness of bridge deck are generated from power spectral density (PSD) function by assuming the roadway as "Average Road". A three dimensionally modeled 5-axle tractor-trailer with its gross weight, which is the same as that of KL-510 design truck, is used for dynamic analysis. For the finite element modeling of superstructure, beam element for the main girder, shell element for the concrete deck, and rigid link between main girder and concrete deck are used. Impact factor and DLA of steel plate girder bridges for different span are calculated by the proposed numerical analysis model and compared with those specified by several bridge codes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.859-865
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• 2007

This paper presents a method to analyze the unbalance response of a high speed polygon mirror scanner motor supported by sintered bearing and flexible supporting structures by using the finite element method and the mode superposition method. The appropriate finite element equations for polygon mirror are described by rotating annular sector element using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. The rotating components except for the polygon mirror are modeled by Timoshenko beam element including the gyroscopic effect. The flexible supporting structures are modeled by using a 4-node tetrahedron element and 4-node shell element with rotational degrees of freedom. Finite element equations of each component of the polygon mirror scanner motor and the flexible supporting structures are consistently derived by satisfying the geometric compatibility in the internal boundary between each component. The rigid link constraints are also imposed at the interface area between sleeve and sintered bearing to describe the physical motion at this interface. A global matrix equation obtained by assembling the finite element equations of each substructure is transformed to a state-space matrix-vector equation, and both damped natural frequencies and modal damping ratios are calculated by solving the associated eigenvalue problem by using the restarted Arnoldi iteration method. Unbalance responses in time and frequency domain are performed by superposing the eigenvalues and eigenvectors from the free vibration analysis. The validity of the proposed method is verified by comparing the simulated unbalance response with the experimental results. This research also shows that the flexibility of supporting structures plays an important role in determining the unbalance response of the polygon mirror scanner motor.