• 정보저장시스템학회논문집
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• 제1권1호
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• pp.23-28
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• 2005

This paper investigates the effects of disk thickness and Pemto slider on PES(position error signal) for high TPI(track per inch) drives above 150kTPI at early stage of their development. In order to reduce the disk flutter which becomes a dominant contributor to the TMR, the thicker disks with both 63 and 69mi1 have been used. Also, PES of a Pemto slider with thinner thickness than Pico slider has been estimated to decrease the conversion factor of disk motion in axial direction to head off-track motion. A frequency-domain PES estimation and prediction tool has been developed via measurement of disk flutter and HSA(head stack assembly) forced vibration. It has been validated by the measured PES in drive level. Based on the model and measurement of disk flutter, PES of a drive with the thicker disk and Pemto slider is predicted and their impact is investigated.

• 대한조선학회지
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• 제8권1호
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• pp.41-52
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• 1971

In this paper, the authors describe not only the linear-theoretical considerations of the hull forms which many schalors have been investigating by the hydrodynamics as to the rolling ships in the waves, but also measure the rolling angles of the models, the coefficients of the effective wave slopes, the forced rolling moments by the waves, the extinctive curves, and the amplitudes of the waves in view of changing both the drafts and the metacentres so that they may study the inclinations of models in the grinoll motion. Owing to the conclusions of these studies, we can learn the fact that the experimental results of the models in the waves agree almost to the linear-theoretical subjects.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권4호
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• pp.409-421
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• 2016

Container ships are prone to move at a greater speed compared to other merchant ships. The slenderness of the hull of container vessel is for better speed, but it leads to unfavorable motions. The pitch and roll are related and sometimes the vessel might be forced to parametric roll condition which is very dangerous. A fin attached to the ship hull proves to be more efficient in controlling the pitch. The fin is fitted at a lowest possible location of the hull surface and it is at the bow part of the ship. Simulations are done using proven software package ANSYS AQWA and the results are compared. Simulations are done for both regular and irregular seas and the effect of fin on ship motion is studied. P-M spectrum is considered for various sea states.

• Coupled systems mechanics
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• 제6권4호
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• pp.439-464
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• 2017

The hydro-elastic system consisting of a pre-stretched highly elastic plate, compressible Newtonian viscous fluid, and the rigid wall is considered and it is assumed that on the plate a lineal-located time-harmonic force acts. It is required to investigate the dynamic behavior of this system and determine how the problem parameters and especially the pre-straining of the plate acts on this behavior. The elasticity relations of the plate are described through the harmonic potential and linearized (with respect to perturbations caused by external time-harmonic force) form of these relations is used in the present investigation. The plane-strain state in the plate is considered and the motion of that is described within the scope of the three-dimensional linearized equations of elastic waves in elastic bodies with initial stresses. The motion of the fluid is described by the linearized Navier-Stokes equations and it is considered the plane-parallel flow of this fluid. The Fourier transform with respect to the space coordinate is applied for a solution to the corresponding boundary-value problem. Numerical results on the frequency response of the interface normal stress and normal velocity and the influence of the initial stretching of the plate on this response are presented and discussed. In particular, it is established that the initial stretching of the plate can decrease significantly the absolute values of the aforementioned quantities.

• 대한물리의학회지
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• 제17권2호
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• pp.29-40
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• 2022

PURPOSE: This study examined the effects of an exercise program for the thoracic spine and scapula rather than the neck, which is the primary site of pain. METHODS: Thirty-two elementary school teachers with a forward head posture (FHP) were assigned randomly to either the experimental group (n = 16) or the control group (n = 16). The experimental group performed scapular stabilization exercise (SSE) and thoracic extension exercise (TEE), and the control group performed cervical self-myofascial release exercise and stretching exercise. The pulmonary functions, pain, craniovertebral angle (CVA), and cervical range of motion (CROM) were measured before the intervention and six weeks after. RESULTS: The within-group comparisons showed that the VAS and CROM (except for extension) in both groups were significantly different before and after the intervention (p < .05). The changes in the maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP), forced vital capacity (FVC), forced expiratory volume at 1 sec (FEV1), and CVA were significant only in the experimental group (p < .05). The between-group comparisons showed a significant difference in the FVC, FEV1, VAS, CVA, and left lateral flexion (p < .05). CONCLUSION: The combination of SSE and TEE in the experimental group was more effective in improving the FHP and breathing ability. Moreover, the experimental group and control combination appeared to be effective in reducing pain and improving the CROM. The combination of SSE and TEE, which are exercises that do not target the cervical spine directly, was effective in improving the posture, respiration, neck pain, and CROM in elementary school teachers with FHP.

• 한국자동차공학회논문집
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• 제2권1호
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• pp.116-127
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• 1994

A method using the linear matrix algebra is developed in order to determine unknown external forces in linear structural analyses. The method defines a matrix which represents the linearity of the vibrational analysis for a structural system. The unknown external forces are determined by the operations of the matrix. The method is applied to find an engine motion in an automobile system. For a simulation process, an exhaust system is modeled and analyzed by the finite element method. The validity of the simulation is verified by comparing with the experimental results the free vibration. Also, an experiment on the forced vibration is performed to determine the damping ratio of the exhaust sysetm. Estimated model parameters(natural frequency, mode shape) are in accord with the experimental results. Because the method merely repeats the transpose and inverse operations of a matrix, the solution is extremely easy and simple. Moreover, it is more accurate than the existing methods in that there is no artificial assumptions in the calculation processes. Therefore, the method is found to be reliable for the analysis of the exhaust system considering the characteristics of vibrations. Although the suggested method is tested by only the exhaust system here, it can be applied to general structures.

• 한국통신학회논문지
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• 제26권10B호
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• pp.1382-1389
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• 2001

움직임 보상-이산 코사인 변환 (motion compensation-discrete cosine transform : MC-DCT) 기반의 동영상 부호화 기법이 부호화 효율성 및 구현의 단순성으로 인해 널리 사용되고 있으나, 에러 환경에서 구조적으로 취약한 면이 있다. 본 논문에서는 다중 메모리 움직임 보상 예측 (long-term memory motion compensated prediction : LTMP) 기반의 다중 레프런스 프레임을 사용하여 에러에 강인한 동영상 부호화 기법을 제안한다. 또한 제안하는 알고리듬에 기반한 에러 은닉 기법 (error concealment : EC)을 구현한다. 즉, R-D (rate-distortion) 최적화에 프레임간 움직임 벡터 (temporal motion vectors)의 확산 인자를 추가하여 에러에 대한 강인성 및 에러 은닉 기법의 효율성을 증가시켰다. 또한, 제안하는 알고리듬은 시간축상의 에러 전파를 피드백 정보 (negative acknowledgement : NAK)를 사용하여 억제한다. 즉, NAK는 채널 에러에 의해 손실된 영역과 에러가 전파된 영역을 추정하여 움직임 보상 영역에서 제외되도록 하는데 이용된다. 따라서, 제안하는 알고리듬은 PSNR 측면에서 FIU (forced intra update)에 근사하는 성능을 보이나, FIU와는 달리 비트율의 증가를 피할 수 있어 제한된 대역폭의 네트웍을 효율적으로 사용할 수 있다. 컴퓨터 모의 실험을 통해 제안하는 알고리듬이 기존의 H.263 및 LTMP 기반의 부호기에 비해 에러 환경에서 주관적 및 객관적 화질 측면에서 성능이 우수함을 보인다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.33-34
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• 2015

북극항로(NSR)를 통항하는 상선과 화물량이 매년 중가추세에 있다. 쇄빙선의 도움을 받아 북극항로를 통항하는 상선의 안전한 항해를 위협하는 가장 큰 요인은 얼음과의 충돌이다. 따라서 선박과 얼음의 충돌 메커니즘을 규명하기 위한 노력이 관련 연구자들에 의해서 활발히 이루어지고 있다. 본 연구에서는 북극항로를 운항하는 내빙선과 유빙의 충돌을 가정한 예인수조실험을 실시하며, 충돌 후 얼음의 운동(속력, 궤적)을 머신비전검사를 통해서 계측한다. 아울러 오차계산을 통해서 머신비전검사 기법의 정밀도를 검증한다.

• 터널과지하공간
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• 제6권2호
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• pp.157-165
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• 1996

In order to analyze the effects of ground vibration caused by underground blasting having an effect on structure, the particle velocity and acceleration are calculated by using DYNPAK program. The DYNPAK program analyzes nonlinear transient dynamic problem and adopts the very popular and easily implemented, explicit, central difference scheme. In this program, the material behavior is assumed to be elasto-viscoplastic. Using the particle acceleration history, modal analysis method is applied to the forced vibration response of multiple-degree-of-freedom(MDOF) systems using unclupled equations of motion expressed in terms of the system's natural circular frequencies and modal damping factors. AS a means of evaluating the vibration behavior of building structure subjected to underground blasting, the time response of the displacements relative to the ground of five-story building is determined. It is concluded that the amount of explosives consumed per round, the location of structure, the properties of rock medium, the stiffness fo structure, etc. act on the important factors influencing on the safety of building and that the response of a structure subjected to a forced excitation can usually be obtained with reasonable accuracy by the modal analysis of only a few mode of the lower frequencies of the system.

• 대한기계학회논문집
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• 제16권9호
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• pp.1711-1721
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• 1992

본 연구에서는 Nayfeh등과 이원경과 소강영은 조화가진하의 핀과 꺽쇠로 고정 된 보(hinged-clamped beam)의 강제 진동 해석을 통하여 점근적으로 안정한 정상상태 응답이 둘 이상 존재할 수 있음을 알게 되었다. 본 연구에서는 이 경우에 접근적으 로 안정한두 정상상태 응답을 구하고 이들 안정한 해로 각각 흡인되는 초기조건들의 집합인 흡인영역을 보간사상법(interpolated mapping method)과 직접 수치적분에 의해 구한 후 서로 비교하였다.