• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.602-607
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• 1997

Ball balance belong to a kind of automatic balancers opten referred to as direct balancer or passive mass systems. In such systems the balancing is achieved with free masses. One of the most prevalent problems encountered in washing is the vibration during spin cycle. The primary cause of this vibration is mass unbalance associated with non unform distribution of clothes. Front loading type machine of European style, especially, has inherent unbalance mass due to its shape and this then makes the vibration worse than top loading type machine, which is more popular in Korea. Since the mass distribution of cloths is random and can not be predicted in advance, direct automatic balances appear to be the only feasible alternative. The results form computer simulation and experimental testing will be presented together with stability implications.

• Smart Structures and Systems
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• 제11권6호
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• pp.623-635
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• 2013

This paper investigates application of a control algorithm called model predictive sliding mode control (MPSMC) to active vibration suppression of a cantilevered aluminum beam. MPSMC is a relatively new control algorithm where model predictive control is employed to enhance sliding mode control by enforcing the system to reach the sliding surface in an optimal manner. In previous studies, it was shown that MPSMC can be applied to reduce hysteretic effects of piezoelectric actuators in dynamic displacement tracking applications. In the current study, a cantilevered beam with unknown mass distribution is selected as an experimental test bed in order to verify the robustness of MPSMC in active vibration control applications. Experimental results show that MPSMC can reduce vibration of an aluminum cantilevered beam at least by 29% regardless of modified mass distribution.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.460-465
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• 2002

The nonlinear vibration of the CRT shadow mask is analyzed in consideration of the V-shaped tension distribution and the effect of wire impact damping. The reduced order FEM model of the shadow mask is obtained from dynamic condensation for the mass and stiffness matrices. Damping wire is modeled using the lumped parameter method to effectively describe its contact interactions with the shadow mask. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. The analysis model of the shadow mask with damping wires is experimentally verified through impact tests of shadow masks performed in a vacuum chamber. Using the validated analysis model of the shadow mask with damping wires, the‘design of experiments’technique is applied to search fur the optimal damping wire configuration so that the vibration attenuation of the shadow mask is maximized.

• 한국소음진동공학회논문집
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• 제12권8호
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• pp.639-647
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• 2002

The nonlinear vibration of the thin perforated plate is analyzed in consideration of the V-shaped tension distribution and the effect of wire impact damping. The reduced order FEM model of the tension plate is obtained from dynamic condensation for the mass and stiffness matrices. Tension wire is modeled using the lumped parameter method to effectively describe its contact interactions with the plate. The nonlinear contact-impact model is composed of spring and damper elements, of which parameters are determined from the Hertzian contact theory and the restitution coefficient, respectively. From the evaluation of the computational accuracy and computation time for the deduced impact stiffness and damping coefficient, we determined proper values for the simulation works, accounting for the computational accuracy as well as the computational efficiency. Finally we discussed the results of nonlinear nitration analysis for variations of their design parameters.

• Structural Engineering and Mechanics
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• 제86권2호
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• pp.237-247
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• 2023

Fourier series-based models in the time domain are frequently established to represent individual bouncing loads, which neglects the stochastic property of human bouncing activity. A power spectral density (PSD) model in the frequency domain for individual bouncing loads is developed herein. An experiment was conducted on individual bouncing loads, resulting in 957 records linked to form long samples to achieve a fine frequency resolution. The Welch method was applied to the linked samples to obtain the experimental PSD, which was normalized by the bouncing frequency and the harmonic order. The energy, energy distribution center, and energy distribution shape of the experimental PSD were investigated to establish the PSD model. The proposed model was used to analyze structural vibration responses using stochastic vibration theory, which was verified via field measurements. It is believed that this framework can evaluate the vibration capacity of structures excited by bouncing crowds, such as concert halls and grandstands.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.826-830
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• 2004

Fault tolerant control method for 6-pole homopolar magnetic bearings are presented. If some of the coils or power amplifiers suddenly fail, the remaining coil currents change via a novel distribution matrix such that the same magnetic forces are maintained before and after failure. Lagrange multiplier optimization with equality constraints is utilized to calculate the optimal distribution matrix that maximizes the load capacity of the failed bearing. Some numerical examples of distribution matrices are provided to illustrate this control method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.279-285
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• 1997

In this paper, the validity for the application of the diffuse sound field theory to the real sound filed, especially on the bounding surfaces of the rooms, was studied. Numerical simulations using ray tracing technique for two models, namely spheres and a reverberant room, were performed. Calculation results show that the distribution of the incident sound energy vs incident angles is approximated to Gaussian distribution, not to the uniform distribution.

• Wind and Structures
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• 제38권3호
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• pp.215-229
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• 2024

Guyed mast structures exhibit characteristics such as high flexibility, low mass, small damping ratio, and large aspect ratio, leading to a complex wind-induced vibration response mechanism. This study analyzed the time- and frequency-domain characteristics of the wind-induced response of a guyed mast structure using measured acceleration response data obtained from the Shenzhen Meteorological Gradient Tower (SZMGT). Firstly, 734 sets of 1-hour acceleration samples measured from 0:00 October 1, 2021, to 0:00 November 1, 2021, were selected to study the vibration shapes of the mast and the characteristics of the generalized extreme value (GEV) distribution. Secondly, six sets of typical samples with different vibration intensities were further selected to explore the Gaussian property and modal parameter characteristics of the mast. Finally, the modal parameters of the SZMGT are identified and the identification results are verified by finite element analysis. The findings revealed that the guyed mast vibration shape exhibits remarkable diversity, which increases nonlinearly along the height in most cases and reaches a maximum at the top of the tower. Moreover, the GEV distribution characteristics of the 734 sets of samples are closer to the Weibull distribution. The probability distribution of the structural wind vibration response under strong wind is in good agreement with the Gaussian distribution. The structural response of the mast under wind loading exhibits multiple modes. As the structural response escalates, the first three orders of modal energy in the tower display a gradual increase in proportion.

• Steel and Composite Structures
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• 제34권2호
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• pp.215-226
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• 2020

The aim of this study is to investigate free vibration of functionally graded porous nanocomposite rectangular plates where the internal pores and graphene platelets (GPLs) are distributed in the matrix either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. The GPL-reinforced plate is modeled using a semi-analytic approach composed of generalized differential quadrature method (GDQM) and series solution adopted to solve the equations of motion. The proposed rectangular plates have two opposite edges simply supported, while all possible combinations of free, simply supported and clamped boundary conditions are applied to the other two edges. The 2-D differential quadrature method as an efficient and accurate numerical tool is used to discretize the governing equations and to implement the boundary conditions. The convergence of the method is demonstrated and to validate the results, comparisons are made between the present results and those reported by well-known references for special cases treated before, have confirmed accuracy and efficiency of the present approach. New results reveal the importance of porosity coefficient, porosity distribution, graphene platelets (GPLs) distribution, geometrical and boundary conditions on vibration behavior of porous nanocomposite plates. It is observed that the maximum vibration frequency obtained in the case of symmetric porosity and GPL distribution, while the minimum vibration frequency is obtained using uniform porosity distribution.

• 한국산학기술학회논문지
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• 제20권8호
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• pp.181-189
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• 2019

항공기용 전원 분배 장치는 발전기에서 생성된 전원을 분배 및 제어하고, 과전류를 보호하는 역할을 한다. 항공기 비행 중에 교류 전원 분배 장치의 결함으로 인해 교류 전원 분배가 불가능해지는 현상이 다수 발생하였다. 이로 인해 정상적인 교류 전원 분배가 불가능하고 일부 전자장비가 구동을 상실하는 문제점이 제기되었다. 본 논문에서는 결함 발생 조건인 항공기 비행 중 진동 조건을 진동 시험 장비로 모의하여, 결함의 근본 원인을 도출한 과정을 기술하였다. 이를 통해 결함의 원인이 교류 전원 분배 장치의 접촉기가 진동에 의해 내부 배선 손상이 발생한 것임을 확인하였으며, 결함 해소를 위해 접촉기 개선 형상을 도출하였다. 또한 결함이 내재된 접촉기를 검출하기 위해, 진동 시험 장비를 활용한 결함 검출 시험을 수행하는 방식으로 시험 절차를 개선하였다. 개선활동 결과 교류 전원 분배 장치의 결함 현상이 개선되었음을 구성품 인증 시험 및 비행 시험을 통해 입증하였다.