• 제어로봇시스템학회논문지
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• 제11권9호
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• pp.741-749
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• 2005

This paper presents a nonlinear controller design for optical disk drive systems to improve anti-shock performance. The nonlinear anti-shock controller is added parallel to the original linear servo control loop. In the previous work, a dead-zone nonlinear element is used for the nonlinear controller and a PID control method is used for the linear controller. Although this parallel structure of the controller improves anti-shock performance, it has a narrow stability bound. In this paper, the dead-zone with saturation nonlinear element is proposed for the nonlinear controller. Since this nonlinear element improves stability margin, we can use higher slope gain of dead-zone than that of nonlinear controller using dead-zone only. In the linear controller design, it is shown that the lead-lag control has an improved stability margin over PID control. Numerical simulation results and experimental results show that the proposed method can get better performance to the external shock than previously proposed methods.

• 정보저장시스템학회논문집
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• 제5권2호
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• pp.76-81
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• 2009

Mobile devices have become an important part of daily life. This is especially true of laptop PCs, which are portable enough to be used almost anywhere. Laptop PCs, however, cannot be nomadic if each component is not robust enough to endure rugged laptop operating environment. Generally, external shock makes collision on head-disk interface and damage to read-write performance. To minimize the likelihood of failure, shock analysis must be incorporated into the design of hard disk drive in laptop. This research explores the structure modification of laptop HDD base, for improving shock performance using finite element analysis which considers the flexibility of whole HDD structure. FE model is verified by modal test and finely tuned. Then we obtained the transmitted acceleration of spindle and pivot and the relative displacement between disk and slider head as shock response. Based on shock simulation, the structural dynamics modification is performed and the primary design parameters are extracted.

• 대한조선학회논문집
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• 제57권1호
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• pp.8-14
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• 2020

The implosion phenomena of pressure vessels operating in deep water under extremely high external pressure have been well known. The drastic energy release to ambient field in the form of pressure pulse is accompanied with catastrophic collapse of shell structure. Such a proximity shock wave could be a serious threat to the structural integrity of adjacent submerged body and several suspected accidents have been reported. In this study, basic research for the occurrence and development of shock wave due to implosion was carried out. The mechanism of pressure pulse generation and energy dissipation were investigated, and a simplified kinematic model to approximate the collapse modes of circular tubes which can be generated by external pressure and implosion was examined. Using the simplified kinematic model, the process of energy dissipation was formulated, and the magnitude of released pressure shock wave was estimated quantitatively. To investigate the validity of developed kinematic model and shock wave estimation process, the results from a nonlinear FE analysis code and collapse test carried out using pressure chamber were compared with the results from the developed kinematic model.

• 한국전산유체공학회지
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• 제19권3호
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• pp.69-76
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• 2014

The shock buffet on a transonic transport aircraft are negative factors that reduce the aerodynamic performance of aircraft. The parametric studies were performed for position of nacelle/pylon to estimate the trend of flow mechanism under the wing that affects shock buffet. To generate external mesh of aircraft configuration that change the position of nacelle, snappyHexMesh provided in OpenFOAM was applied. Implicit density-based solver(ISAAC) was used for flow analysis. The change of nacelle position along horizontal direction dynamically affected the aerodynamic performance of transonic transport aircraft as comparing that of vertical direction. As a result of the parametric study of nacelle/pylon position, it was confirmed that the optimal position of nacelle can be obtained by aerodynamic design.

• 정보저장시스템학회논문집
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• 제9권2호
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• pp.51-55
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• 2013

HDD has been easily exposed to the external shock and vibration because HDD has to apply to mobile devices. Therefore, the stiffness of base has been the important factors for the design of HDD. To improve the stiffness of base, the frame was applied to the base. First, the finite element model of the base was constructed. Then, the FE model was verified by modal analysis. Drop test was performed to confirming the shock simulation model. The dynamic characteristic of original base which is verified is compared with the base which is applied the frame through modal analysis and shock analysis.

• 한국시스템다이내믹스연구
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• 제10권3호
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• pp.47-79
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• 2009

The paper examines dynamic relationship among 'Limit to Growth' factors in Korea using causal loop diagram. It also aims to explore policy implications for Korea in overcoming current difficulties and future crisis we may face. For this purpose, five factors -economy, population, resource, environment, food- used in the were adopted as an analytical framework. Findings show that Korea is fragile to external shock such as world economic crisis, food price surge, and resource price -including energy price- hike. High dependency of energy, food and resource on foreign market was found to be a major source of limit to growth in Korea. Furthermore, environmental problems like global warming could be a major external shock that could hit Korea harder than the rest of the world. Policy implications and measures for these problems were discussed too.

• Journal of the Korean Data and Information Science Society
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• 제25권1호
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• pp.65-76
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• 2014

주택가격은 정부의 부동산 정책이나 국내외의 경기상황과 같은 외부충격요인에 따라 많은 영향을 받는다. 본 연구에서는 주택가격지수 예측을 위한 모형구축에서 중요한 요인은 외부충격요인으로 이를 개입효과라 하며, 이 외부요인들이 주택가격지수에 미치는 영향을 파악하고 향후 주택가격지수를 효율적으로 예측하기 위한 시계열모형을 찾는데 있다. 실제 자료를 이용하여 분석한 예측결과 개입모형이 다른 모형에 비해 우수한 것으로 나타났다.

• 한국정밀공학회지
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• 제16권4호통권97호
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• pp.46-56
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• 1999

A semi-actively controlled impact system which adjusts an impulse exerted by the external impact is studies. The main control variables are internal pressure difference inside the cylinder and the shock absorber displacement while it travels. Compared to a conventional one so called a passive system with a variable orifice inside the cylinder, a semi-actively controlled system utilizes an external orifice controlled by a highly fast responding electrical proportional valve. This device overcomes the temperature and viscosity change due to continuous operating and keeps the desired pressure difference and displacement in every operation. In this article a new prototype impact system is designed and manufactured based on a semi-actively control system. Through computer simulations and experiments, we verify the possibility of controlling the shock absorber pressure and displacement. After investigating the control performance a modified semi-actively controlled system with better control performance is also proposed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.622-625
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• 2008

SIL-based optical disk drive will be promising candidate of next-generation storage devices. However, a near-field optical disk drive requires the robustness to external shock because of extremely small gap between SIL and media. Especially, high-level shock damages permanently to SIL and it makes difficulties in general application. To study the likelihood of failure, the shock analysis must be performed over all others. This research explores the dynamic characteristics of rotating disk through FEM which is compared to analytical solution and experimental modal analysis. We also develop the finite element model of an optical disk drive, which includes rubber mounts, sled base, rotating disk and pickup assembly, and simulate the shock response.

• 한국항공우주학회지
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• 제50권5호
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• pp.297-308
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• 2022

극초음속 영역에서 운용되는 대부분의 극초음속 공기흡입(Air-breathing) 비행체들에 스크램제트 엔진이 탑재되고 있다. 스크램제트(Scramjet) 엔진에서는 일반적인 가스터빈 엔진의 압축기 역할을 흡입구에서 발생하는 충격파가 대신 수행하기 때문에 충격파에 의한 전압력 손실이 매우 중요하게 여겨진다. 본 연구에서는 전압력 손실을 최소화하기 위해 등엔트로피 압축면을 적용한 외부 압축형 흡입구의 설계법을 제시하고, 동일한 조건의 Busemann 흡입구와 3개의 cone 각도를 가지는 외부 압축형 흡입구를 설계하였다. 이후 전산해석을 통해 비설계 조건에 대한 성능 특성을 비교하였다. 각 흡입구 형상은 3단 외부 압축형 흡입구의 길이에 맞춰 truncation을 진행하였으며, 경계층 보정을 수행하였다. 등엔트로피 외부 압축형 흡입구는 3단 외부 압축형 흡입구에 비해 설계점에서는 우수한 성능을 보였으나 일부 비설계 조건에서는 3단 외부 압축형보다 성능이 저하되는 현상이 발생하였다.