• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2002.05a
• /
• pp.543-548
• /
• 2002

Nowadays since the customers of HDD's are interested in their noise levels in addition to their primary performances such as their average access time, capacity, HDD manufacturers make efforts on reducing the noise. The works to reduce noise are usually based on the measurable physical quantities such as SPL or acoustic intensity level. However, since the HDD noise is Judged by human beings, the basis of noise reduction should be human sensations. In this paper, the noise levels of various HDD's are evaluated by the human jury test to find a relationship between the physical quantities used for noise control and the human sensations of noise. Discrepancies are found in the judgments by the human beings and by the physical quantities. The loudness level, a psychoacoustic variable, is used to solve the discrepancy.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.1
• /
• pp.103-112
• /
• 2007

Recently structures become longer and higher because of the developments of new materials and construction techniques. However, such modern structures are susceptible to excessive structural vibrations, which may induce problems of serviceability and structural damages. In this paper we attempt to control structural vibration using the probabilistic neural network(PNN) and the artificial neural network(ANN) based on the training pattern that consist of only the structural state vector and the control force. The state vectors of the structure and control forces made by linear quadratic regulator(LQR) algorithm are used for training pattern of PNN and ANN. The proposed algorithm is applied for the vibration control of the three story shear building under Northridge earthquake. Control results by the proposed PNN and ANN are compared with each other.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.763-768
• /
• 2012

Active window system which can reduce the environmental noises, such as traffic noise and construction noise, from an open window into a room was proposed in the previous works. The key idea of the proposed active window system was that the control sources are approximately collocated with the primary noise source in terms of the acoustic power for global noise reduction throughout the interior room. Moreover, because it is important not to intrude into the living space in the building environment, no error sensors were used and an open-loop control method using control sources at the window frame and the reference sensors outside the room was used for the proposed system. The open-loop control gain was calculated by the interior room model assumed as the semi-infinite space, and the interior sound field was estimated by Rayleigh integral equation under the baffled window model assumption. However, windows with a finite thickness should were considered for the calculation of the open-loop control gain of the active window system since these are representative of most window cases. Therefore, the finite thickness window model based on the Sgard's model was derived and the open-loop control gain using the interior sound field estimated by that model was calculated for active window system. To compare the performance of these two models, a scale-model experiment was performed in an anechoic chamber according to noise source directions. Experimental results showed that the performance for the thickness window model is better than the baffled window model as the angle with respect to the perpendicular direction is larger.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.6 no.3
• /
• pp.88-96
• /
• 1998

The rattle noise is the most significant in many kinds of manual gearbox nioses, which is generated at the idle stage of the engine operation. The main torsional vibrat- ion source of the driveline is the fluctuation of the engine torque. The gear rattle is impacts generating in the backlash of the free gear due to this torsional vibration. Many researchers reported the clutch torsional characteristic optimization method to reduce the idle gear rattle but only few of them give sufficient consideration to the system parameters like gear backlash, drag torque, system inertia, inertia distribution, engine torque fluctuation, idle engine rotation speed, and accessory load. In this paper, influence rate of system parameters on the gear rattle is presented and counterplans like backlash reduction, drag torque increase, inertia addition, inertia distribution modification and engine torque characteristic control are suggested.

• Explosives and Blasting
• /
• v.8 no.4
• /
• pp.3-22
• /
• 1990

The $\varphi{4.5}$ meters pilot tunneling work is almost done to the $\varphi{11.3}$ meters twin tunnel of NAM SAN No1. The south side pit of 400 meters is weak zone of Rock status, so client request us to allow the cautious blasting pattern for drilling on the condition of 0.2 kine vibration allowance limited for the safety of side running tunnel. The pattern of cautious blasting carried out by 6 time divided fiving on the round drilling depth of 1.20 meters(1.10) and also applied control blasting method with line drilling due to the reduction of vibration.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.3 no.3
• /
• pp.63-74
• /
• 1999

A sliding mode fuzzy control (SMFC) algorithm is presented for vibration of large structures. Rule-base of the fuzzy inference engine is constructed based on the sliding mode control, which is one of the nonlinear control algorithms. Fuzziness of the controller makes the control system robust against the uncertainties in the system parameters and the input excitation. Non-linearity of the control rule makes the controller more effective than linear controllers. Design procedure based on the present fuzzy control is more convenient than those of the conventional algorithms based on complex mathematical analysis, such as linear quadratic regulator and sliding mode control(SMC). Robustness of presented controller is illustrated by examining the loop transfer function. For verification of the present algorithm, a numerical study is carried out on the benchmark problem initiated by the ASCE Committee on Structural Control. To achieve a high level of realism, various aspects are considered such as actuator-structure interaction, modeling error, sensor noise, actuator time delay, precision of the A/D and D/A converters, magnitude of control force, and order of control model. Performance of the SMFC is examined in comparison with those of other control algorithms such as $H_{mixed 2/{\infty}}$ optimal polynomial control, neural networks control, and SMC, which were reported by other researchers. The results indicate that the present SMFC is an efficient and attractive control method, since the vibration responses of the structure can be reduced very effectively and the design procedure is simple and convenient.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.270-275
• /
• 1995

본 논문에서는 3자유도를 갖는 2차원 강체날개의 플러터 속도를 향상시키는 축차 제어기를 설계하는 기법을 연구하였다. 먼저 2차원 강체날개의 운동방정식을 유도하고 플러터 해석을 수행하였다. 다음 수동계의 플러터 속도를 향상시키는 능동제어기를 설계한 후 제어기의 차수를 축차하는 기법을 적용하여 저차의 능동제어기를 구성하였다. 제어기 축차기법으로는 BACR을 사용하였으며 전차 제어기의 상태변수를 약 80%정도 줄일 수 있다. 축차된 제어기를 사용한 능동시스템과 전차 제어기를 사용한 능동시스템의 제어효과의 차이는 무시 할 수 있을 정도로 매우 작다. 따라서, BACR을 사용하여 얻은 축차된 제어기를 사용하면 상당한 계산량 감소효과와 실시간 단축효과를 얻을 수 있음을 확인하였다. 또한 동일한 돌풍입력에 대한 각각의 능동 시스템의 시간응답도 매우 양호한 결과를 얻을 수 있었으며, 전차 제어기를 사용한 능동시스템의 돌풍응답과 축차된 제어기를 사용한 능동시스템의 돌풍 응답 사이의 차이도 매우 작게 나타났다. 그러므로, 항공기 날개의 능동 플러터억제에는 BACR을 이용하여 설계한 축차된 제어기가 플러터 능동제어에 매우 유용하다고 할 수 있다. 그러나 BACR을 사용하기 위해서는 요구되는 정확도와 계산량에 대한 상호 절충과정이 반드시 필요하다.

• Earthquakes and Structures
• /
• v.7 no.6
• /
• pp.1171-1186
• /
• 2014

Damping is one of the parameters that control the performance of structures when they are subjected to seismic, wind, blast or other transient shock and vibration disturbances. By adding supplemental viscous dampers, the energy input from a transient deformation is absorbed, not only by the structure itself, but also by the supplemental dampers. The aim of this study is to evaluate the values of both damping and ductility reduction factors for steel moment resisting frames with supplemental linear viscous dampers. Two-dimensional finite element models have been established for a range of low to mid rise buildings with different parameters: number of floors; number of bays; and number of dampers with different supplemental damping ratios (from 5% to 30%). A parametric study has been performed using time history analyses and a well-documented research method (N2-method). In addition, an equation has been proposed for each reduction factor based on regression analysis for the obtained results. The results of the Time history analyses are compared with those of a modified N2-method. Moreover, a comparison with values specified in the European code EC8 and the Egyptian code ECP-201 has been performed.

• Structural Engineering and Mechanics
• /
• v.24 no.3
• /
• pp.275-290
• /
• 2006

In this paper, the performance of a tuned liquid damper (TLD) in suppressing the seismic response of buildings is investigated with shake table testing of a four-story steel frame model that rests on pile foundation. The model tests were performed in three phases with the steel frame structure alone, the soil and pile foundation system, and the soil-foundation-structure system, respectively. The test results from different phases were compared to study the effect of soil-structure interaction on the efficiency of a TLD in reducing the peak response of the structure. The influence of a TLD on the dynamic response of the pile foundation was investigated as well. Three types of earthquake excitations were considered with different frequency characteristics. Test results indicated that TLD can suppress the peak response of the structure up to 20% regardless of the presence of soils. TLD is also effective in reducing the dynamic responses of pile foundation.

• Journal of the Korean Solar Energy Society
• /
• v.36 no.6
• /
• pp.1-12
• /
• 2016

A control algorithm for a 100 kW wind turbine is designed in this study. The wind turbine is operating as a variable speed variable pitch (VSVP) status. Also, this wind turbine is a permanent magnet synchronous generator (PMSG) Type. For the medium capacity wind turbine considered in this study, it was found that the optimum tip speed ratios to achieve the maximum power coefficients varied with wind speeds. Therefore a commercial blade element momentum theory and multi-body dynamics based program was implemented to consider the variation of aerodynamic coefficients with respect to Reynolds numbers and to find out the power and thrust coefficients with respect tip speed ratio and blade pitch angles. In the end a basic power controller was designed for below rated, transition and above rated regions, and a load reduction algorithm was designed to reduce tower vibration by the nacelle motion. As a result, damage equivalent Load (DEL) of tower fore-aft has been reduced by 32%. From dynamic simulations in the commercial program, the controller was found to work properly as designed. Experimental validation of the control algorithm will be done in the future.