• Smart Structures and Systems
• /
• 제4권5호
• /
• pp.697-710
• /
• 2008

Long steel stay cables, which are mainly used in cable-stayed bridges, are easy to vibrate because of their low inherent damping characteristics. A lot of methods for vibration reduction of stay cables have been developed, and several techniques of them have been implemented to real structures, though each has its limitations. Recently, it was reported that smart (i.e. semi-active) dampers can potentially achieve performance levels nearly the same as comparable active devices with few of the detractions. Some numerical and experimental studies on the application of smart damping systems employing an MR fluid damper, which is one of the most promising smart dampers, to a stay cable were carried out; however, most of the previous studies considered only one specific control algorithm in which they are interested. In this study, the performance verification of MR fluid damper-based smart damping systems for mitigating vibration of stay cables by considering the four commonly used semi-active control algorithms, such as the control algorithm based on Lyapunov stability theory, the maximum energy dissipation algorithm, the modulated homogeneous friction algorithm and the clipped-optimal control algorithm, is systematically carried out to find the most appropriate control strategy for the cable-damper system.

• 한국멀티미디어학회논문지
• /
• 제12권1호
• /
• pp.130-138
• /
• 2009

컴퓨터와 함께 많은 시간을 보내는 현대인들 중에는 바탕화면과 화면보호기로 마음의 편안함을 주는 자연풍경이나 가상수족관 등을 설정하는 사용자들이 증가하고 있다. 가상수족관은 임의의 가상 해저환경에서 자유롭게 행동하는 여러 종류의 물고기를 만들고, 동작을 분석하여, 물고기들의 애니메이션 작업을 수행함으로써 만들어진다. 본 논문에서는 유체의 형태변화를 실시간으로 표현하는 유체 애니메이션 기법과 가상물고기의 다양한 속성에 따라 상호작용을 할 수 있는 Smart Fish기술을 이용하여 활용가치가 높은 실감형 가상수족관을 구축하는 방법을 제안했다. 본 논문에서 제안하는 방법은 다양한 해저환경을 표현하는 가상수족관, 수족관 화면 보호기, 물고기 육성 게임 등에 활용되어질 수 있다.

• 한국유체기계학회 논문집
• /
• 제14권2호
• /
• pp.25-28
• /
• 2011

The control rod assemblies do freely fall into the reactor core by the gravity from the control rod drive mechanism. In order to achieve a rapid shutdown and control the reactor power, it is required to insert control rod assemblies as soon as possible. In this paper, we evaluated the drop time and flow characteristics caused around guide tube for SMART(System-integrated modular advanced reactor) control rod assembly. Numerical analyses are carried out with FLUENT program of computational fluid dynamics. This study results show that the drop time of the control rod assembly in the operating condition of SMART is more 20 percent rapidly than the drop time of the room temperature and ambient atmosphere condition.

• 스마트미디어저널
• /
• 제4권2호
• /
• pp.9-16
• /
• 2015

Fluids appear in innumerable phenomena; therefore, it is interesting to reproduce those phenomena by computer graphics techniques. However, this process is not trivial. We work with a fluid simulation that uses Navier-Stokes equations to model the fluid, a semi-Lagrangian approach to solve it and the level set method to track the surface of the fluid. Modified versions of the Navier-Stokes equations for computer graphics allow us to create a wide diversity of effects. In this paper, we propose a technique that allows us to integrate a force inspired by surface tension into the model. We describe which information we need and how to modify the model with this new approach. We end up with a modified simulation that has additional effects that might be suitable for computer graphics purposes. The effects that we are able to recreate are small waves and droplet-like formations close to the surface of the fluid. This model preserves the overall behavior governed by the Navier-Stokes equations.

• Tribology and Lubricants
• /
• 제29권1호
• /
• pp.39-45
• /
• 2013

Magnetorheological (MR) fluid belongs to the group of smart materials. In MR fluid, iron particles in base oil form chains in the direction of the applied magnetic field, thus resulting in a variation in the stiffness and damping characteristics of the fluid. Research is being carried out on controlling the stiffness and damping characteristics as well as the tribological characteristics of the MR fluid. In this study, the friction characteristics of MR fluid have been evaluated using three types of materials and magnetic fields of different strengths. The coefficients of friction of the three types of MR fluid are measured, and the relationship between the coefficient of friction and the strength of the applied magnetic field is obtained.

• 한국초전도ㆍ저온공학회논문지
• /
• 제26권1호
• /
• pp.25-30
• /
• 2024

High-temperature superconducting rotors offer advantages in terms of output-to-weight ratio and efficiency compared to conventional phase conduction motors or generators. The rotor can be cooled by conduction cooling, which attaches a cryocooler, and by refrigerant circulation, which uses circulating liquid or gas neon, helium and hydrogen. Recent work has focused on environmental issues and on high-temperature superconducting motors cooled with liquid hydrogen that can be combined with fuel cells. However, to ensure smooth supply and return of the cryogenic cooling fluid, a cryogenic rotational coupling between the rotating and stationary parts is necessary. Additionally, the development of a sealing structure to minimize fluid leakage applicable to the coupling is essential. This study describes the design and performance evaluation of a non-contact sealing method, specifically a labyrinth seal, which avoids power loss and heat load caused by friction in contact sealing structures. The seal design incorporates a spiral flow path to reduce leakage using centrifugal force, and computational fluid dynamics (CFD) simulations were conducted to analyze the flow path and rotational speed. A performance evaluation device was configured and employed to evaluate the designed seal. The results of this study will be used to develop a cryogenic rotational coupling with supply and return flow paths for cryogenic applications.

• 대한기계학회논문집
• /
• 제17권7호
• /
• pp.1649-1657
• /
• 1993

This paper reports on a proof-of-concept experimental investigation focused on evaluating the vibration characteristics and control of smart hollow cantilever beams filled with an electro-rheological(ER) fluid. The beams are considered to be of uniform viscoelastic materials and modelled as a viscously-damped harmonic oscillator. Electric field-dependent natural frequencies, loss factors and complex moduli are evaluated and compared among three different beams : two types of different volume fraction of ER fluid and one type of different particle concentration of ER fluid by weight. Modal characteristics of the beams are observed in both the absence and the presence of electric potentials. It is also shown that by constructing active control algorithm the removal of structural resonances and the suppression of tip deflection are obtained. This result provides the feasiblility of ER fluids as an active vibration control element.

• 드라이브 ㆍ 컨트롤
• /
• 제1권1호
• /
• pp.40-49
• /
• 2004

• 한국소음진동공학회논문집
• /
• 제13권8호
• /
• pp.612-618
• /
• 2003

A hybrid vibration control scheme using ER fluid and PZT patches is proposed. Dynamic characteristics of the beam embedded with the ER fluid can be controled by changing the strength of the electric field applied on the ER fluid, thus provides a mean to avoid the resonance. It was found that active vibration control of the structure embedded with ER fluid failed to suppress the vibration excited with broad band frequency due to the limited change of the dynamic characteristics of the structure. To compensate this limited effect of the control scheme with ER fluid alone, PPF control using PZT patches as sensors and actuators is added to construct a hybrid controller. Experimental results suggests that proposed hybrid controller is effective to suppress the additional resonance vibration that appears when each controller is used alone.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
• /
• pp.451-455
• /
• 1997

This paper presents vibration mode control of a smart plate containing electro-rheological (ER) fluid between elastic face layers. Following the composition of a silicone oil-based ER fluid, the ER fluid-embedded plate partitioned into four sections is constructed. Then, an extensive modal test is experimentally carried out to identify field-dependent modal parameters such as mode shapes and natural frequencies of the structure with respect to different are subjected to electric fields. The distilled results from the experiment exhibit that the ER fluid can be effectively employed in a continuous fashion to tune modal behaviors of the distributed parameter systems,