• 대한기계학회논문집B
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• 제28권6호
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• pp.619-627
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• 2004

In most industrial applications, the geometrical complexity is combined with the moving boundaries. These problems considerably increase the computational difficulties since they require, respectively, regeneration and deformation of the grid. As a result, engineering flow simulation is restricted. In order to solve this kind of problems the immersed boundary method was developed. In this study, the immersed boundary method is applied to the numerical simulation of stationary, rotating and oscillating cylinders in the 2-dimensional square cavity. No-slip velocity boundary conditions are given by imposing feedback forcing term to the momentum equation. Besides, this technique is used with a second-order accurate interpolation scheme in order to improve the accuracy of flow near the immersed boundaries. The governing equations for the mass and momentum using the immersed boundary method are discretized on the non-staggered grid by using the finite volume method. The results agree well with previous numerical and experimental results. This study presents the possibility of the immersed boundary method to apply to the complex flow experienced in the industrial applications. The usefulness of this method will be confirmed when we solve the complex geometries and moving bodies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.69-74
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• 2001

It is well known that an air bubble trapped in water emits light at its collapse robustly with a proper forcing amplitude of ultrasound. Instability mechanism which causes deviation from sphericity of bubble wall was investigated theoretically. The rapid change of the bubble wall velocity which is both dependent on the forcing amplitude, was found to be a major factor of instability of the interface. The Rayleigh-Taylor instability which occurs when rapid acceleration is directed from the lighter towards the heavier fluid is found to be not related to the instability of the sonoluminescing gas bubble. A good agreement between the calculation results and experimental data is found.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.265-270
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• 2001

This study presents a feedback control methodology for suppression of the vortex shedding from a circular cylinder in a uniform flow. A rotational oscillation is applied as a controlled forcing and the lift coefficient ($C_L$) is used as a feedback signal. A feedback control concept is made based on the phase relation between the rotation velocity and $C_L$ at 'lock-on', The phase between the forcing and the vortex formation is changed $180^{\circ}$ from the phase of enhancing the lock-on state. This concept is examined by solving the Van del Pol equation. The results are satisfactory.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.148-153
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• 2001

A computational investigation of the effect of the electromagnetic force(or Lorentz force) on the flow behavior around a circular cylinder, a typical model of bluff bodies, is conducted. Two-dimensional unsteady flow computation for $Re=10^2$ is carried out using a numerical method of finite difference approximation in a curvilinear body-fitted coordinate system by solving the momentum equations including the Lorentz force as a body force. The effect of the spatial variations of the Lorentz forcing region and forcing direction along the cylinder circumference is investigated. The numerical results show that the Lorentz force can effectively suppress the flow separation and oscillation of the lift force of the circular cylinder cross-flow, leading to the reduction of the drag.

• 한국전산유체공학회지
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• 제17권2호
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• pp.71-77
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• 2012

Numerical simulations are carried out for flow over a circular cylinder controlled by the momentum forcing which is generated by a pair of plasma actuators symmetrically mounted on the cylinder surface. A popular and empirical plasma model is used for the spatial distribution of momentum forcing. In this study, we consider two different types of actuation, i.e., steady and unsteady (or pulsed) actuation. In the unsteady actuation, the actuation is turned on and off periodically, its frequency being a control parameter. The objective of this study is to investigate the effects of actuator location and actuation frequency on the flow structures and the forces on the cylinder. Results show that the cylinder wake can be effectively controlled by proper actuator location. For example, when the actuators are located at $120^{\circ}$ from the stagnation point, vortex shedding is completely suppressed with the boundary layer almost fully attached to the surface, resulting in drag reduction and lift elimination.

• 한국소음진동공학회논문집
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• 제12권8호
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• pp.609-615
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• 2002

본 논문에서는 단순하고 효율적인 학습제어 로직을 운동기구용 로봇팔 시스템에 적용하였다. 일반적으로 운동시에 운동기구에 적용되는 힘은 사용자마다 다르고 같은 사용자라 하더라도 운동시마다 다를 것이다. 이미 사용자의 신체조건에 따라 입력된 최적의 힘과 실제 가해지는 힘 사이의 오차를 보상하는데 본 논문에서는 학습제어를 적용하여 가해지는 힘의 종류(시변 또는 시불변함수)와 상관없이 빠르게 오차를 제거하고 원하는 운동을 추종함을 시뮬레이션을 통하여 확인할 수 있었다.

• Structural Engineering and Mechanics
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• 제74권4호
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• pp.515-520
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• 2020

In the modern era, the world is facing unprecedented challenges in form of environmental pollution and international agencies are forcing scientists and materialists to look for green materials and structures to counter this problem. Composites based on renewable sources like plant based fibres, vegetable fibres are finding increasing use in interior components of automobile vehicles, aircraft, and building construction. In the present study, jute and flax fibre based composites were developed and tested for assessing their suitability for possible applications in interior cabin and parts of automobile and aerospace vehicles. Matrix system involves epoxy as resin and fibre weight fractions used were 45% and 55% respectively. Composites samples were prepared as per American society for testing and materials (ASTM) standard and were tested for individual fiber tensile strength, composite tensile strength, and flexural strength to analyse its behavior under various loading conditions. The results revealed that the Jute fibre composites possess enhanced mechanical properties over Flax fibre composites.

• 한국전산구조공학회논문집
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• 제28권5호
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• pp.477-483
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• 2015

본 논문에서는 Euler-Bernoulli Beam(EB-beam) 및 신속 Fourier 변환을 이용하여 수치분석적 빔 모델 및 Co-rotational plane beam EDISON program(CR-beam)을 이용한 빔 모델의 가진주파수 변화에 따른 외팔보의 자유단 진동 연구를 수행하였다. 위의 두 빔 모델에서의 끝단에서는 진동이 시간이 지남에 따라 감소하다가 정상상태에 이르는 것을 확인하였다. 끝단에서 가진주파수가 증가함에 따라 구조적 감쇠에 의해 변위이 감소하는 경향을 보인다. 감쇠를 고려한 EB-beam과 CR-beam가 정상상태로 진입하는 경향이 비슷하나, 가진주파수는 정상상태가 나타나는 시간과 독립적임을 제시한다.

• Journal of Mechanical Science and Technology
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• 제20권6호
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• pp.849-863
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• 2006

IBM (Immersed Boundary Method) with feedback momentum forcing was applied to stationary and moving bodies. The capability of IBM to treat the obstacle surfaces, especially with moving effect has been tested for two dimensional problems. Stationary and oscillating cylinders were simulated by using IBM based on finite volume method with Cartesian coordinates. For oscillating cylinder, lateral and vertical motions are considered, respectively. Present results such as time histories of drag and lift coefficients for both stationary and oscillating cases are in good agreement with previous numerical and experimental results. Also, the instantaneous wake patterns of oscillating cylinder with different oscillating frequency ratios well represented those of previous researches. More feasibility study for IBM has been carried out to two oscillating cylinders. Drag and lift coefficients are presented for two cylinders oscillating sinusoidally with phase difference of $180^{\circ}$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.74-74
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• 2003