• Smart Structures and Systems
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• v.16 no.6
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• pp.1023-1047
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• 2015

In this study, the optimal location of the MR fluid segments in a partially treated laminated composite sandwich plate has been identified to maximize the natural frequencies and the loss factors. The finite element formulation is used to derive the governing differential equations of motion for a partially treated laminated composite sandwich plate embedded with MR fluid and rubber material as the core layer and laminated composite plate as the face layers. An optimization problem is formulated and solved by combining finite element analysis (FEA) and genetic algorithm (GA) to obtain the optimal locations to yield maximum natural frequency and loss factor corresponding to first five modes of flexural vibration of the sandwich plate with various combinations of weighting factors under various boundary conditions. The proposed methodology is validated by comparing the natural frequencies evaluated at optimal locations of MR fluid pockets identified through GA coupled with FEA and the experimental measurements. The converged results suggest that the optimal location of MR fluid pockets is strongly influenced not only by the boundary conditions and modes of vibrations but also by the objectives of maximization of natural frequency and loss factors either individually or combined. The optimal layout could be useful to apply the MR fluid pockets at critical components of large structure to realize more efficient and compact vibration control mechanism with variable damping.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1255-1263
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• 2000

In this study, the modification of turbulent boundary layer flow by local wall vibration is investigated. The wall is locally vibrated using a wall deformation actuator, which moves up and down at the frequencies of 100Hz and 50Hz. Simultaneous measurements of the streamwise velocities in the spanwise direction are performed at several wall-normal and streamwise locations using an in-house multi-channel hot wire anemometer and a spanwise hot-wire-probe rake. The mean velocity is reduced in most places due to the wall vibration and its reduced amount becomes small as flow goes downstream. Interestingly, the mean velocity is found to increase very near the wall and near the actuator. This is due to the motion induced by the streamwise vortices which are generated by the downward motion of the actuator. In case of the streamwise velocity fluctuations, their magnitude increases as compared to the unperturbed turbulent boundary layer, and the increased amount becomes small as the flow moves downstream. The modified flow field at the forcing frequency of 50Hz is not much different from that of 100Hz, except the reduced amount of modification.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.9-12
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• 2001

Composite materials can be used economically and efficiently in broad civil engineering applications when standards and processes for analysis, design, fabrication, construction and quality control are established. Many of the bridge systems, including the girders and cross-beams, and concrete decks behave as the special othotropic plates. Such systems with boundary conditions other than Navier or Levy solution types, or with irregular cross sections, analytical solution is very difficult to obtain. Numerical method for eigenvalue problems are also very much involved in seeking such a solution. A method of calculating the natural frequency corresponding to the first mode of vibration of beam and tower structures with irregular cross-sections was developed and reported by the author in 1974 Recently, this method was extended to two dimensional problems including composite laminates, and has been applied to composite plates with various boundary conditions with/without shear deformation effects and reported at several international conferences including the Eighth Structures Congress of American Society of Civil Engineers in 1990. In this paper, the result of application of this method to the special orthotropic plates with various boundary condition is presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.370-377
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• 2000

This paper presents a mixed-mode type ER(electro-rheological) engine mount, and its vibration control performance for a passenger vehicle is presented. The field-dependent yield stress of a transfo rmer oil-based ER fluid is empirically distilled in both shear and flow modes. This is then incorporated with the governing equation of motion of the proposed mixed-mode(shear mode plus flow mode) type engine mount. The damping force is analyzed with respect to the intensity of the electric field and design parameters such as electrode gap. Subsequently, the ER engine mount which is equivalent to the conventional hydraulic engine mount in terms of the damping level is designed and manufactured. Both computer simulation and experimental test are undertaken in order to evaluate vibration isolation performance. In addition, this performance is compared with that of the conventional hydraulic engine mount.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.5
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• pp.734-741
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• 2003

This paper addresses the vibration mode shape Measurement technique utilizing a Continuous Scanning Laser Doppler Vibrometer (CSLDV). The continuous scanning capability is added to the conventional discrete Laser Doppler Vibrometer by reflecting the laser beams on the surface of the object using two oscillating mirrors. The bow scanning resulted from the proposed scanning method is eliminated by feedback control. The velocity output signal from the CSLDV is modulated to give the spatial velocity distribution in terms of coefficients which are obtained from the Fast Fourier Transformation of the time dependent velocity signal. Using the Chebyshev series from, the analysis of the vibration mode shape techniques for straight line scanning and 2 dimensional scanning are presented and discussed. The performance of the proposed SLDV is presented using the experimental results of the vibration mode shape of a cantilever and plate

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1991.04a
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• pp.169-173
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• 1991

최근 자동화기술의 발달에 따라 산업용 로보트팔의 경량화, 고속화를 실행하 게 되는 경우와 우주, 원자력발전소 등과 같은 특수한 환경하에서 매니퓰레 이터(manipulator)를 제어하게 되는 경우가 많아지고 있는데, 이때 팔의 강성 이 충분하지 않으면 위치결정시 목표점에서의 과도진동이 발생하게 되어 위 치결정정도와 작업효율이 저하된다. 그러므로 이러한 경량화된 장비들의 진 동특성을 파악하고 운동시 발생하는 진동을 효율적으로 제어할 수 있는 제 어기(controller)를 설계하여 잔류진동을 감쇠시키므로써 위치결정시간을 줄 일 수 있고, 전체 작업행정시간이 단축되므로써 작업ㅎ류을 향상시키는 효과 를 가져오게 된다. 이때 원하고자 하는 제어를 하기 위해서는 제어대상 (plant)의 계규명(system identification)을 정확히 하여야 하는데 해석적으로 계를 규명하기가 까다로운 경우 제어기를 설계하는 것이 사실상 어렵게 되 므로 이러한 경우 실험적인 방법으로 주파수응답함수(frequency response function)를 구해 계의 모형(model)을 구하는 방법이 널리 사용되고 있다. 이 분야에 있어서 기존의 논문들은 팔의 변위를 측정하여 진동을 제어하나 이 러한 방법들은 간헐적으로 움직이는 산업장비(예:로보트의 팔)의 과도응답을 제어하기에는 부적합하다. 따라서 본 연구에서는 이러한 장비들의 과도응답 을 효과적으로 제어할 수 있도록 가속도계를 사용, 가속도를 측정하여 변위 를 제어하고자 한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.375-380
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• 2007

This paper presents optimal design of controllable magnetorheological (MR) shock absorbers for passenger vehicle. In order to achieve this goal, two MR shock absorbers (one for front suspension; one for rear suspension) are designed using an optimization methodology based on design specifications for a commercial passenger vehicle. The optimization problem is to find optimal geometric dimensions of the magnetic circuits for the front and rear MR shock absorbers in order to improve the performance such as damping force as an objective function. The first order optimization method using commercial finite element method (FEM) software is adopted for the constrained optimization algorithm. After manufacturing the MR shock absorbers with optimally obtained design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of conventional shock absorbers. In addition, vibration control performances of the full-vehicle installed with the proposed MR shock absorbers are evaluated under bump road condition and obstacle avoidance test.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.452-458
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• 2007

The vertical extension of a building in general remodeling process increases both gravity and seismic loads by simply adding masses to the building. In this study, a vertical extension structural module (VESM) is proposed for enhancing seismic performance of the existing buildings by utilizing the story-increased parts. The proposed VESM is composed of steel column, steel beam, and beam-end rotational damper. The steel columns are connected to the shear walls and transfer the wall rotation in out-of plane to the steel beam, and then the beam-end rotational damper dissipates the earthquake-induced energy. Numerical analysis result from a cantilever beam of which end-rotation is restricted by rotational damper indicates that the displacement, base shear, and base overturning moment of the existing structures showing cantilever behavior can be significantly reduced by using the proposed method. Also, it is observed that friction-type rotational damper is effective than viscous one.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.43-50
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• 2002

In the design of structure, the forces acting on tai structure are key parameter fur noise and vibration control. However, in the complex structure, the forces at the injection point on the structure cannot be measured directly. So, it is necessary to find out Indirect force evaluation method. In this paper, forces have been measured with In-situ vibration responses and system information. And, three existing techniques of indirect force measurement, vita. direct inverse. principal component analysis and regularization have been compared. This paper shows that multi-vibration responses are essential for talc precise estimation of the forces. To check these conditions, rotary compressor is adopted as test sample, because it is very difficult to measure the injection forces from internal excitation to shell. It alas also been obtained that relatively higher force is transmitted through three welding paths to the compressor shell. It shows a good agreement between direct and indirect force evaluation with curvature shell and plate.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.221-224
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• 2004

A theoretical model has been studied to describe the sound radiation analysis for structure vibration noise of vehicle tires under the action of random moving line forces. When a tire is analyzed, it had been modeled as curved beams with distributed springs and dash pots that represent the radial , tangential stiffness and damping of tire, respectively. The reaction due to fluid loading on the vibratory response of the curved beam is taken into account. The curved beam is assumed to occupy the plane y=0 and to be axially infinite. The curved beam material and elastic foundation are assumed to be lossless Bernoulli-Euler beam theory including a tension force, damping coefficient and stiffness of foundation will be employed. The expression for sound power is integrated numerically and the results examined as a function of Mach number, wave-number ratio and stiffness factor. The experimental investigation for structure vibration noise of vehicle tire under the action of random moving line forces has been made. Based on the Spatial Transformation of Sound Field techniques, the sound power and sound radiation are measured. Results strongly suggest that operation condition in the tire material properties and design factors of the tire govern the sound power and sound radiation characteristics.