• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.5 s.122
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• pp.464-471
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• 2007

This paper presents a maneuver analysis of a full-vehicle featuring electrorheological(ER) suspension and ER brake. In order to achieve this goal, an ER damper and an ER valve pressure modulator are devised to construct ER suspension and ER brake systems, respectively. After formulating the governing equations of the ER damper and ER valve pressure modulator, they are designed and manufactured for a middle-sized passenger vehicle, and their field-dependent characteristics are experimentally evaluated. The governing equation of motion for the full-vehicle is then established and integrated with the governing equations of the ER suspension and ER brake. Subsequently, a sky-hook controller for the ER suspension and a sliding mode controller for the ER brake are formulated and implemented. Control performances such as vertical displacement and braking distance of vehicle are evaluated under various driving conditions through computer simulations.

• Structural Engineering and Mechanics
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• v.63 no.4
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• pp.537-549
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• 2017

One of the main concerns of civil engineering researchers is developing or modifying an energy dissipation system that can effectively control structural vibrations, and keep the structural response within tolerable limits during unpredictable events like earthquakes, wind and any kind of thrust load. This article proposes a new type of mass damper system for controlling wideband earthquake vibrations, called Multiple Wall Dampers (MWD). The basic principle of the Tuned Mass Damper (TMD) was used to design the proposed wall damper system. This passive energy dissipation system does not require additional mass for the damping system because the boundary wall mass of the building was used as a damper mass. The multi-mode approach was applied to determine the location and design parameters of the dampers. The dampers were installed based on the maximum amplitude of modes. To optimize the damper parameters, the multi-objective optimization Response Surface Methodology was used, with frequency response and maximum displacement as the objective functions. The obtained structural responses under different earthquake forces demonstrated that the MWD is one of the most capable tools for reducing the responses of multi-storied buildings, and this system can be practically used for new and existing building structures.

• Structural Engineering and Mechanics
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• v.47 no.2
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• pp.149-166
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• 2013

Flexible behaviors in new aerospace structures can lead to a degradation of their control and guidance system and undesired performance. The objectives of the current work are to analyze the vibration resulting from the propulsion force on a Single Stage to Orbit (SSTO) launch vehicle (LV). This is modeled as a follower force on a free-free Euler-Bernoulli beam consisting of two concentrated masses at the two free ends. Once the effects on the oscillation of the actuators are studied, a solution to reduce these oscillations will also be developed. To pursue this goal, the stability of the beam model is studied using Ritz method. It is determined that the transverse and rotary inertia of the concentrated masses cause a change in the critical follower force. A new dynamic model and an adaptive control system for an SSTO LV have been developed that allow the aerospace structure to run on its maximum bearable propulsion force with the optimum effects on the oscillation of its actuators. Simulation results show that such a control model provides an effective way to reduce the undesirable oscillations of the actuators.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.387-393
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• 2001

Installing vibration control devices in the structure rises as a solution instead of increasing structural strength considering construction cost. Especially, viscoelastic dampers show excellent vibration control performance at low cost and are easy to install in existing structures compared with other control devices. Therefore, cost-effectiveness of structure with viscoelastic dampers needs to be evaluated. Previous cost-effectiveness evaluation method for the seismically isolated structure(Koh et al., 1999;2000)is applied on the building structure with viscoelastic dampers, which combines optimal design and cost-effectiveness evaluation for seismically isolated structures based on minimum life-cycle cost concept. Input ground motion is modeled in the form of spectral density function to take into account acceleration and site coefficients. Damping of the viscoelastic damper is considered by modal strain energy method. Stiffness of shear building and shear area of viscoelastic damper are adopted as design variables for optimization. For the estimation of failure probability, transfer function of the structure with viscoelastic damper for spectral analysis is derived from the equation of motion. Results reveal that cost-effectiveness of the structure with viscoelastic dampers is relatively high in how seismic region and stiff soil condition.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.8
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• pp.856-863
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• 2008

High-rise apartments of shear wall system are governed by flexural behavior like a cantilever beam. Installation of the damper-brace system in a structure governed by flexural behavior is not suitable. Because of relatively high lateral stiffness of the shear wall, a load is not concentrate on the brace and the brace cannot perform a role as a damping device. In this paper, a friction damper applying flexibility of shear wall is proposed in order to reduce the deformation of a structure. To evaluate performance of the proposed friction damper, nonlinear time history analysis is executed by SeismoStruct analysis program and MVLEM(multi vertical linear element model) be used for simulating flexural behavior of the shear wall. It is found that control performance of the proposed friction damper is superior to one of a coupled wall with rigid beam. In conclusion, this study verified that the optimal control performance of the proposed friction damper is equal to 45 % of the maximum shear force inducing in middle-floor beam with rigid beam.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.63-67
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• 2009

The previous work (Cheong et al., 2006) where the characteristics of acoustic emissions of wind turbines has been investigated according to the methods of power regulation, has showed that the acoustic power of wind turbine using the stall control for power regulation is more correlated with the wind speed than that using the pitch control. In this paper, basically extending this work, the noise generation characteristics of large modern upwind wind turbines are experimentally indentified according to the power regulation methods. To investigate the noise generation mechanisms, the distribution of noise sources in the rotor plane is measured by using the Beam-forming measurement system (B&K 7768, 7752, WA0890) consisting of 48 microphones. The array results for the 660 kW wind turbine show that all noise is produced during the downward movement of the blades. This result show good agreement with the theoretical result using the empirical formula with the parameters: the convective amplification; trailing edge noise directivity; flow-speed dependence. This agreement implies that the trailing edge noise is dominant over the whole frequency range of the noise from the 660 kW wind turbine using the pitch control for power regulation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.892-896
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• 2001

Investigation is performed on the stability of nonlinear system under turbulent fluid motion modelled as white noise random process, which is a preliminary result in the course of research on the characteristic and nonlinear control of the stochastic system. Adopted physical model is beam-type structure with tip-mass and main base mass. The governing equation is derived via F-P-K approach in stochastic sense. By means of Gaussian Closure method infinite dynamic moment equations due to system nonlinearity is closed to finite one. At the best of authors' knowledge, it is the first trial to design nonlinear controller by using of sliding mode technique in stochastic domain and control performance and effect in stochastic domain is studied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1990.10a
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• pp.53-58
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• 1990

The use of spreadsheet packages for solving noise control problems has been cited by several authors, eg Saha[1] and Thornton[2]. The effectiveness of using spreadsheet packages compared with the traditional computer programs written in high level languages was demonstrated when applied to relatively simple problems, such as the selection of hearing protectors or the prediction of noise equation which includes logarithmic additions at most represents the physics of the problem. The simplicity of the governing equation together with the requirement to handle a vast amount of data are considered to be the major reasons for noise control engineers to use spreadsheet packages. Although shipboard noise prediction seems to be very complicated, the calculation procedure itself is, in essence, identical especially true for prediction methods based on empirical formulae[3,4], ie the procedure that consists of the three basic elements, ie source, path and receiver. This paper discusses the application of spreadsheet package LOTUS 1-2-3 to shipboard noise prediction problems. A utility program of the package is written using macro functions and is shown to be especially useful for noise control engineers who are unfamiliar with spreadsheet packages. In addition, a new type of empirical formula, to estimate structureborne noise transmission loss, is proposed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.869-873
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• 2008

Optimization method for the open loop commutation time intervals in HDD spindle start-up control is presented in this paper. A hard disk drive(HDD) uses a sensorless brushless DC motor(BLDC) for the platter rotation. Because there is no direct sensor for the rotor position, open loop commutations after sensing the rotor position at a standstill using inductive sensing method are performed to speed up the rotor up to a certain speed where the zero crossings of the back electromotive force(EMF) are measurable. Therefore successful open loop commutations are necessary for the stable start-up control of the spindle motors. Random neighborhood search(RNS) algorithm is introduced as a optimization technic in this paper. Rotor speed and its standard deviation are used as a cost function and commutation intervals obtained from the spindle motion equation are used as initial parameter values for the RNS. With the help of the proposed method optimized open loop commutation time intervals for the very low start-up current are acquired and tested. The experimental results shows that the proposed method can decrease the start-up failure rate of a HDD spindle motor.

• Journal of KSNVE
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• v.8 no.4
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• pp.632-642
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• 1998

A method based on finite element discretization is developed for optimizing the polarization profile of PVDF film to create the modal transducer for specific modes. Using this concept, one can design the modal transducer in two-dimensional structure having arbitrary geometry and boundary conditions. As a practical means for implementing this polarization profile without repoling the PVDF film the polarization profile is approximated by optimizing electrode patterns, lamination angles, and poling directions of the multi-layered PVDF transducer. This corresponds to the approximation of a continuous function using discrete values. The electrode pattern of each PVDF layer is optimized by deciding the electrode of each finite element to be used or not. Genetic algorithm, suitable for discrete problems, is used as an optimization scheme. For the optimization of each layers lamination angle, the continuous lamination angle is encoded into discrete value using binary 5 bit string. For the experimental demonstration, a modal sensor for first and second modes of cantilevered composite plate is designed using two layers of PVDF films. The actuator is designed based on the criterion of minimizing the system energy in the control modes under a given initial condition. Experimental results show that the signals from residual modes are successfully reduced using the optimized multi-layered PVDF sensor. Using discrete LQG control law, the modal peaks of first and second modes are reduced in the amount of 12 dB and 4 dB, resepctively.