• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2960-2967
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• 2021

In this work, a new hardening model is proposed for the depth-dependent hardness of ion-irradiated polycrystals with obvious grain size effect. Dominant hardening mechanisms are addressed in the model, including the contribution of dislocations, irradiation-induced defects and grain boundaries. Two versions of the hardening model are compared, including the linear and square superposition models. A succinct parameter calibration method is modified to parametrize the models based on experimentally obtained hardness vs. indentation depth curves. It is noticed that both models can well characterize the experimental data of unirradiated polycrystals; whereas, the square superposition model performs better for ion-irradiated materials, therefore, the square superposition model is recommended. In addition, the new model separates the grain size effect from the dislocation hardening contribution, which makes the physical meaning of fitted parameters more rational when compared with existing hardness analysis models.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.407-413
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• 2008

This paper investigates the dynamics of a HDD spindle system due to the change of FDBs. Flying height of the HDD spindle system is determined through the static analysis of the FDBs, and the stiffness and damping coefficients are calculated through the dynamic analysis of the FDBs. Free vibration characteristics and shock response of the HDD spindle system are analyzed by using the finite element method and the mode superposition method. Experimental modal test is also performed to verify the accuracy of the proposed method. This research shows that the stiffness coefficients of journal heating mostly affect the rocking frequencies because their magnitude are within the range of the stiffness of supporting structure. It also shows that the damping coefficients of thrust bearing mostly affect the axial frequency because the stiffness of thrust bearing is much smaller that that of supporting structure.

• 한국기계가공학회지
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• 제19권3호
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• pp.36-41
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• 2020

Mechanical systems installed in transport devices, such as vehicles, airplanes, and ships, are mostly subject to translational accelerations at the joints during operations. This base acceleration excitation has a large influence on the performance of the system, therefore, its response must be well analyzed. However, the existing methods for dynamic analysis of structures have some limitations in use. This study presents a new numerical method using relative acceleration to solve these limitations. If the governing equation of motion is linear and the mass matrix, the damping matrix, and the stiffness matrix are constant over time in the finite element analysis, the proposed method can be applied to the transient behavior analysis and the harmonic response analysis of the structure. Because it is not necessary to introduce a virtual mass and the rigid body motions are removed from the analysis, it is possible to use not only the direct integration method in the time domain but also the mode superposition method to obtain the dynamic responses. This paper demonstrates with three examples how the present method is suitable for the dynamic analysis of a structure with multi-degree of freedom.

• 대한조선학회지
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• 제20권1호
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• pp.21-27
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• 1983

The mode superposition method(MSM) for the forced transverse vibration analysis of structures subject to Timoshenko beam analogy, which had originally been developed by Ormondroyd and McGoldrick, is reviewed to formulate it in more general form taking account of rotary inertia, dampings in separate terms of internal and external ones, and simultaneous action of exciting forces and moments. To investigate some general features of the method in practical utilizations, resonant maximum amplitudes of 4 high speed ships under concentrated sinusoidal excitation at the stern are calculated by both MSM and the finite difference method(FDM). For the FDM the hulls are discretized into 40 equal segments, and in utilization of MSM contributions of the first six modes are summed up to obtain responses up to the six-nodes resonant mode. The numerical results show that MSM gives slightly higher values, $4{\sim}10%$, than those by FDM. Since there is always uncertainty in the damping estimation of actual systems, influences of the damping magnitude on resonant amplitudes and a practical method to estimate modal damping coefficients are discussed.

• 한국해양공학회지
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• 제22권1호
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• pp.22-29
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• 2008

A numerical investigation is made on the effects of the location and shape of the front wall of an OWC(Oscillating Water Column) chamber on the hydroelastic response of a VLFS. Most of the studies on the effects of an OWC chamber on the response of a VLFS have assumed the location of the OWC chamber to be at the front of the VLFS. In the present study, an OWC-chamber is introduced at an arbitrary position in relation to a VLFS to determine the influence of the location and shape of the OWC chamber on the hydroelastic response of the VLFS. A finite element method is adopted as a numerical scheme for the fluid domain. or the finite element method, combined with a mode superposition method, is applied in order to consider the change of mass and stiffness The OWC chamber in a piecewise constant manner. or the facilitated anefficient analysis of The hydroelastic response of the VLFS, as well as the easy modeling of different shape and material properties for the structure. Reduction of hydroelastic response of the VLFS is investigated for various locations and front wall shapes of the owe chamber.

• 대한조선학회논문집
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• 제38권4호
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• pp.39-47
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• 2001

본 논문에서는 매트형 거대 부유식 구조물의 동적 응답을 모드중첩법을 이용하여 시간영역에서 해석하였다. 동유체력의 시간기억함수는 고차경계요소법으로 계산한 동유체감쇠력을 푸리에변환하여 구하였으며, 구조물의 동적 응답은 해석적으로 유도한 고유 모드를 시간적분하여 산정하였다. 해석법을 검증하기 위하여 집중하중이 순간적으로 제거되는 경우, 집중하중이 충격적으로 가해지는 경우, 그리고 집중하중이 등속으로 일정거리를 움직인 경우 등 3가지에 대하여 계산을 수행하였다. 이렇게 얻은 수치결과는 3가지 경우 모두 모형에 대한 실험치와 잘 일치하였다.

• Geomechanics and Engineering
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• 제30권4호
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• pp.325-336
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• 2022

This paper analyzes the ground surface settlements induced by side-by-side twin shield tunnels bored in sedimentary soils, which primarily consist of sand with clay strata above the tunnel crown. The measurements were obtained during the construction of twin tunnels underneath the Incheon International Airport (IIA) located in Korea. The measured surface settlement troughs are approximated with Gaussian functions. The trough width parameters i and K of the settlement troughs produced by the first and second tunnel passings are determined, along with those for the total settlement trough. The surface settlement troughs produced by the first shield passing are reasonably represented by a symmetric Gaussian curve. The surface settlement troughs induced by the second shield tunnel display marginal asymmetric shapes at selected sections. The total settlement troughs are fitted both with a shifted symmetric Gaussian function and the superposition method utilizing an asymmetric function for the incremental trough produced by the second tunnel. It is revealed that the superposition method does not always produce better fits with the total settlement. Instead, the shifted symmetric Gaussian function is overall demonstrated to provide more favorable agreements with the recordings. Therefore, the shifted symmetric Gaussian function is recommended to be used in the design for the prediction of the settlement in clays caused by twin tunneling considering the simplicity of the procedure compared with the superposition method. The amount of increase in the width parameter K for the twin tunnel relative to that for the single tunnel is quantified, which can be used for a preliminary estimate of the surface settlement in clay induced by twin shield tunnels.

• 터널과지하공간
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• 제17권6호
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• pp.484-492
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• 2007

국내에서는 주로 환산거리 진동예측식에 의한 발파진동 예측 방법이 사용되고 있다. 그러나 이러한 환산거리방식은 실규모의 발파가 시행되어져야 할 필요성이 있다. 최근 국내에서는 터널 등의 공사 시행 전 사전 조사단계에서 발파진동의 영향권을 예측하려는 시도로서 지질 조사용 시추공 등에 장약 발파하여 지반진동을 측정하고 본 발파의 발파 진동을 예측하는 방법이 사용되고 있다. 그러나 이러한 발파진동 예측 방법은 본 발파시의 진동의 전달 특성을 완전하게 반영하지는 못한다. 이러한 발파진동 예측방법의 결점을 보완하기 위하여 본 연구에서는 사전 조사 단계의 단일공 파형 중첩 모델링을 통하여 발파진동을 예측하는 방법을 개발하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권2호
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• pp.117-126
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• 2016

In this paper, a numerical procedure for the natural vibration analysis of plates with openings and carlings based on the assumed mode method is extended to assess their forced response. Firstly, natural response of plates with openings and carlings is calculated from the eigenvalue equation derived by using Lagrange's equation of motion. Secondly, the mode superposition method is applied to determine frequency response. Mindlin theory is adopted for plate modelling and the effect of openings is taken into account by subtracting their potential and kinetic energies from the corresponding plate energies. Natural and frequency response of plates with openings and carlings subjected to point excitation force and enforced acceleration at boundaries, respectively, is analysed by using developed in-house code. For the validation of the developed method and the code, extensive numerical results, related to plates with different opening shape, carlings and boundary conditions, are compared with numerical data from the relevant literature and with finite element solutions obtained by general finite element tool.

• 한국소음진동공학회논문집
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• 제20권10호
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• pp.915-922
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• 2010

This paper presents an efficient method for determining the forced response of a spinning flexible disk-spindle system supported by fluid dynamic bearings(FDBs) in a computer hard disk drive(HDD). The spinning flexible disk-spindle system is represented by the asymmetric finite element equations of motion originating from the asymmetric dynamic coefficients of the FDBs and the gyroscopic moment of a spinning disk-spindle system. The proposed method utilizes only the right eigenvectors of the eigenvalue problem to transform the large asymmetric finite element equations of motion into a small number of coupled equations, guaranteeing the accuracy of their numerical integration. The results are then back-substituted into the equations of motion to determine the forced response. The effectiveness of the proposed method was verified by comparing it with the responses from the classical methods of mode superposition with the general eigenvalue problems, and mode superposition with modal approximation. The proposed method was shown to be effective in determining the forced response represented by the asymmetric finite element equations of motion of a spinning flexible disk-spindle system supported by FDBs.